N. Banks.
Some Characters in the Perlidæ.
Psyche 54:266-?, 1947.

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SOME CHARACTERS IN THE PERLIDB*
BY NATHAN BANKS
Holliston, Mass.
Many years ago when I started to classify our Perlidae I neglected to study the head, antennae, and legs. In re- cent years others have emphasized the importance of genitalia and nymphal structure. Species are physiolog- ical units, genera are structural units. Reproduction is one of the most important physiological processes, so that the structure of the genital parts is of great value in species. These vary from species to species so that only in a general way can they be used for genera. If the genus is to be something different from the species, it must rest on characters which are not commonly used for species. Species reflect adaptation to environment, the recent and temporary life. Genera should rest on long- inherited structures, of little or no use to the adult, but which reflect heredity; characters common to several species.
The wings of Pteronarcys and Isoperia have many dif- ferences, but for each genus the wing is efficient ; the great number of crossveins in the former genus is not neces- sary, they represent inheritance, not use, and so become of value in the classification of genera or higher groups. Of the several structures that I have observed, the anal lobe of the fore wings1 and a vein (anal brace), arising- from the under side of the anal cell, and crossing the anal lobe seem to me to represent the course of specialization. In Pteronarcys the anal lobe is very large and the anal brace (vein that crosses it) complete and strong. In * Published with a grant from the Museum of Comparative Zoology at Harvard College.
This anal lobe is rarely shown in figures of wings. Figure I in Needham
and Claassen shows the anal area of fore wing but does not indicate the line of fold which separates the anal lobe from the rest of the wing. Many figures indicate the anal brace but often only partially or incorrectly. In the Selys part one, Klapalek on page 6 shows line of fold, in part 2, page 9, he shows the anal brace. N. & 0. on plates 13 and 16 show the anal brace in Perla and Acronewria.
266




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19471 Banks-Characters k the Perlidis 267 Figures 1 to 8 I have indicated the gradual modification until it vanishes in Peltoperla. In Pteronarcys the anal brace extends obliquely backward (recurrent). Other general with an oblique recurrent anal brace are Acro- meuria, Togoperla, Banksiana, Neoperla, Perlesta, Ptero- narcella, Harrisiola,2 Perlinella.
In Isogenus the anal brace arises closer to the base of the anal cell and extends transversely to the margin: other genera in this group are Perlod&, Clioperla, &- droverla. Those in which the anal lobe is very small and folded under and the brace vestigial are ~so~erla, Para- perla, Diploperla, some species placed in Clioperla (I am not sure of genotype). In Atoperla there is a very short basal part of anal brace arising before base of anal cell, often difficult to determine. In many cases the outer part of anal brace is weaker than basal part. In some species of Isoperla the lobe and brace are very small and weak or absent, in few distinct. In five genera the lobe and anal brace are absent : Peltoperia, Alloperia, Chloroperla, Kathroperla, and Hastaperla. In Perlesta, and some- times other forms, the anal brace is bent at the line of fold.
ANTENNB.
The antennae in Perlidae are rarely mentioned except to note the color. Walker, in the descriptions of two species (decolorata and decisa) says antennae "very minutely pubescent " and "brown, minutely pubescent. " The antennae of Pteronarcys and Acromuria have joints near the base very short and broad, some, at least immovable; in Togoperia immarginata it is similar. In Perlodes the joints near base are usually longer, but still broader than long; also in Isogenus and Hydroperla. In many of the species placed by Needham and Claassen in Perla and Clioperla the third joint is plainly longer than the fourth, the latter and several following joints being much broader than long. In this type of antennae the joints are not narrowed at base until much further out 2 Harrisiola (type Peria flavescens Walsh). I we this name for the spe-
cies (except type) that were put by Klapalek in Neophasganophora; the type species being a Perla.




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268 Psyche
[Dec.
where the joints are much longer than broad. In Ptero-
narcella the joints become longer than broad much sooner. In all of these the hairs on the antennae are very small and fine, well described as "minutely pubescent. " Often they are erect, but in some slope toward tip of joint. In Togoperla the hairs, though longer, are closely ap- pressed; in Perlinella, though short, are also appressed. In the genotype of Isoperla (bilkeata) the joints near base are as long as broad, the hairs are very short, but near the tip or beyond the middle is a longer erect hair, which I shall call a sense hair. In other species of Iso- peda it is the same, but a few (ebria) that have some- times been placed in Isoperlu do not have these sense- hairs, or at least not well-developed. In Alloperla, in Perlesta, it is the same as Isoperla. In Neoperla the hairs are longer but the sense-hairs are very prominent, also Diploperla, Paraperla, and Katkroperla, as well as Chloropeda and Hastaperla have them more or less distinct.
In Isogenus and Perlodes there are no sense-hairs or else so small as to be unnoticed, in Hydroperla some spe- cies show very tiny erect hairs toward the tip of the joint, but in others they are very small or absent, in some Diploperla they are also short, but usually distinct and near tip of joint, in Clioperlu (sirnilis, slossom~) they are readily seen. In some Acrmeuria (xanfhenes, cali- fornica) the sense-hairs are fairly distinct, beyond the short joints, in others they are obscure or absent. In the Perlince distinct, but not as prominent as in Neoperla. HEAD.
In shape the head ranges from twice as broad as long (Peltoperla) to twice as long as broad (Paraperla) ; and behind the eyes the head may extend more than twice the diameter of the eye (Kathroperla) or there may be scarcely any space at all (some Hydroperla). The head may be considered as of three areas : occipital area, the part behind eyes and ocelli; the interocular area, and the face or area in front of anterior ocellus. The occipital area is often very short in middle, where it is



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19471 BanksÌÔCharacter in the Perlida 269 separated from the interocular area by a curved line or groove, the occipital line, the ends of which curve for- ward. Just behind the eyes the head usually narrows toward the pronoturn, but in a few forms (Perlodes, Atoperla) the side at first bulges outward before it starts to narrow. In the middle there is frequently a line or groove from the occipital line to the rear of head; this median groove is present in Perlodes, Isogenus, Clioperla, some Isoperla, also in P. nona and obscura. It is short or hidden in Perla (Togo per la), Acroneuria, Harrisiola, Perlinella, Perlesta, Atoperla, Alloperia, but is present in P. luctuosa, P. modesta and P. phalerata. It is present in some very small species as P. ebria. In ~~d~o~eria it is not present, at least in sight, but sometimes a small groove on the hidden part of head or as a very fine line. The occipital line is usually quite distinct in the primi- tive forms; in the more specialized it may show behind the hind ocelli, or be entirely obliterated. In Perlodes it slopes each side and ends in front of eyes ; in Perliptzanes it slopes less and runs into lower part of eye; in Perla and Acroneuria it slopes each side just outside of boss and is stopped by a ridge. In Calliperla it slopes each side a little concavely to a point near eye where it con- nects with a line sloping below inwardly, the outer part of the M-mark. In Harrisiola and Atoperla it makes a full semicircle, the ends running into the boss; in P. modestus it makes a broader curve, also ending in the boss each side, but not a full semicircle. In Isogenus it is lower and broad, stopping near boss.
In ~erl&ella the
sides disappear a little beyond boss.
In Perlesta it con-
nects top of ocelli, beyond vestigial.
In Isoperla it some-
times shows sloping from behind the hind ocelli toward the eye, but more often it is not visible. The interocular area has the three (or two) ocelli. They form a triangle as long or longer than broad in Perla, Acroneuria, Harrisiola, and some Perlodes; in Iso- genus, Pictetia, many Clioperla and Isoperia the triangle is broader than long or at least as broad. The hind ocelli are usually situated at about the middle of the eye-space; in Perlinella and KatJiroperZa a little



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270 Psyche [DW.
behind eyes, in Alloperia further back than usual, and sometimes behind the eyes. In Isogenus, Hpdroperh, Clioperlo, and some related species the hind ocelli look more or less laterally from the head of a broad groove, there being a ridge on their inner edge as high as the ocelli; in Isoperh the hind ocelli look more upward; in Acroneuria, Alloperia, Harrisiola the hind ocelli project above the surface of the head. The distance of the hind ocelli from the eyes is, at most, only a character of species. In nearly ail Perlids there is a small swollen spot a little in front of each hind ocellus, and often further out. This is the lateral tubercle or boss. It is more or less char- acteristic in shape and position for each species. Some- times hardly further than the diameter of the ocellus, again it may be five to ten times as far away. In a few cases it is circular, but usually longer than the ocellus, and one end may be enlarged, or narrowed at outer end. hi front of the anterior oeellus is the face. There is usually a transverse groove or a depressed spot in front of the anterior ocellns. In front of this there is on each side a smooth area, or raised area, usually elongate and sloping outward; frequently they are pyri- form. These are the middle part of what Keedham calls the M-mark; however it is better called the V-mark, since the outer sides are faint or absent in most species. Some- times the two are joined together above in a broad curve. They never reach the front margin of head, and near each lateral corner may be a dark rounded spot. The shape and divergence of the V-mark are very good characters for species and species-groups.
But sometimes widely
separated genera may have the V-mark of very similar shape. I have figured a number of these, and I think they should be considered in descriptive work. In some species the head is without marks, or only dark around the ocelli, lint in many there is a pattern of dark marks, which has long been recognized of specific value. There is, of course, variation in the development of a pat- tern. When the same pattern occurs in two or more spe- cies, there are differences in structure; often in shape of the ocellar triangle or on the lower face.



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1947 I Banks-Characters in the Perlida 271 The head of Perlodes, when viewed from above, shows the side behind each eye somewhat swollen before it be- onins to slope inward. Behind the eye of Isogenus the side is, at first straight, then slopes inward ; in Hydroperla it is less distinct, since the head is shorter behind the eyes, but in ebria and gravitans( ?) the side is plainly promi- nent before sloping. The last two species, when viewed from below, show a somewhat globose area behind the eye. In many species the side behind eye is convex, but it begins to slope at the eye. Perlinella and Calliperla show the side somewhat swollen before the slope. FEMORA.
The femora have on their lower edge a row of short, fine hairs or the hairs may have above them a row of stouter bristles, or the hairs may be more numerous and spreading up on the lower part of the femur, and with bristles interspersed or in a row. Those with the row of short fine hairs are the genera Perlodes (and subgen- era), Isogenus, Hydroperla, Clioperla and Isoperia, the other genera have bristles besides the hairs. In the Perla and Chloroperla sections there are always bristles on the femora, either in a row or among the hairs. In shape the femora may be very long and slender, with nearly parallel sides, but in many of the genera with bristles among the hairs (Perlesta, Neoperla, Calliper- linae) the femora are shorter, broader, and the upper edge convex.
WINGS.
Needham and Claassen in the table to species of Perla use the position of the cubito-anal cross-vein to divide the genus in two sections, one in which this cross-vein is placed its length beyond the end of anal cell, and the other where the cross-vein is at end of cell or only a trifle be- yond. I11 general it would be better to divide whether the cross-vein is at or before end of anal cell, or plainly beyond. The amount beyond varies a bit in some species. It is plainly beyond in Isogewus, Hydroperla, Perlodes, Perlinella. In Pteronarcys this vein is much beyond end of cell, so we may consider this a primitive character.



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272 Psyche [Dec.
However in Isoperla both ways occur commonly, even sometimes in the same specimen.
One point in venation is very interesting, it is the fork- ing of the cubital vein in fore wings; in all but two sub- families the cubitus forks in such a way that the anterior branch diverges at least a little, but plainly, from the main stem while the lower branch either runs out nearly as a continuation of the stem or also diverges from the stem, so if stem were continued it would divide the fork. In two subfamilies, the Isoperlinge and the Chloroperlinae the upper branch runs out as a continuation of the stem and the lower branch definitely diverges from the stem. These two subfamilies, although having much general resemblance, differ so much in details of structure that this similarity in forking of cubitus may be the result of similar needs for strengthening the flight structure. I11 the primitive forms there are more costal cross- veins, and more branches to the radial sector than in more specialized forms, but the result is not constant, but highly variable. One point is of interest, the origin of the radial sector is usually a little beyond the end of the first anal vein, if one moves further out so does the other, Perlinella having both points further out than in Perlesta. How- ever in Perla immargkta., in Perlinella, sometimes in Acroneuria the radial sector arises before end of anal vein, and in Hydroperla and Calliperla luctuosa often opposite. The position of the cord, is usually at begin- ning of outer third, of wing; in Perlesta, Calliperla, some Acroneuria it is before end of second third, while in Per- linella, and in some Clioperla it is beyond end of second third.
In the more primitive genera the subcosta extends out to the cord or near it, and in a few, Acroneuria, Perlodes, Perla, it may extend beyond the cord. In Isogenus, Calli- perla, Harrisiola, Peltoperla, Atoperia, and KatJiroperla it reaches the cord, or nearly so. In Alloperia, Para- perla, Isoperla the subcosta ends well before the cord. Sometimes it may fade out or be very indistinct as in Nunoperla and Perlesta (some species).
The number of veins in the anal area of the hind wings



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19471 Banks-Characters kn the Perlida 273 is normally five, Paraperla has but four, Alloperia three, and Hastaperla has no anal area. In most genera the second and fifth are branched, in some Acroneuria and Perla with several branches.
In the hind wings the number of cubital cross-veins, if more than one, has been used, it varies, but is somewhat useful. The number of branches of the second and last anal veins, is also helpful, but rarely dependable. The length of the union of radial sector and medius has also been used, but too variable for a generic character. PALPI.
The palpi in Pteronarcys, Perla, Acroneuria are short and inconspicuous, the last joint of the maxillary palpi very small, the third somewhat swollen at tip ; in Isogems, the fourth joint is longer, and in some species (nona, ebria, etc.) the palpi are much longer and more slender, the fourth joint prominent and the third joint not swollen at tip, while in Alloperia the last joint is very short, scarcely noticeable.
SETB.
The setae, or tails, in the primitive forms (Perla, Acro- meuria, Peltoperla) are short and in Perla and Acroneuria much thickened at the base and taper to the slender tip. The first few joints in Perla are simple annulations, not real joints; in Acroneuria they are usually more like a joint, plainly separated by a notch on the side ; in Pelto- peria some species are similar to Perla, in others more distinct. Also in Perlodes, and Hydroperlo, some species have short setae, the basal joints scarcely separated. But in most Perlidae the set= are long, often as long as ab- domen, and with many joints much longer than broad, and with long erect bristles near tip of each joint. RESULTS.
On considering these characters in the various genera one sees that there are two primary trends or groups of primitive Perlidae, one the Acroneuria group distin- guished by the oblique anal brace arising from near third anal vein, the other the Isogenus group with an anal brace arising from the base or near base of anal cell and ex-



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274 Psyche [Dec.
tended transversely across anal area and anal lobe when present. In the specialization that occurs in both lines, there comes reduction in venation, reduction in anal lobe, and many modifications that will be of use in the par- ticular group.
Both groups have a fringe of hair on lower edge of the femora, in Perlodes and Isogenus very fine and evenly short, in Acroneuria more dense and with some stiffer and longer bristles. Both groups have the basal antenna1 joints very short, but in each line they become longer in more recent genera. In both lines the anal brace grad- ually weakens and disappears. In the Acroneuria line there is more tendency to retain and develop the bristles ; but bristles appear in some of the fairly primitive genera of the Isogenus line, such as Calliperla and Diploperla; but in the more specialized forms (Isoperla) the bristles disappear, while in the most specialized group (Chloro- ~erlinae) of the Acroneuria line the bristles are most highly developed.
With the numerous similarities, as well as the differ- ences, of structure in the group, it appears to me that in the Plecoptera there are, as Newman in 1853 stated, but three families, Pteronarcidae, Perlidas, and Nemouridae, and that under the Perlidae are eleven subfamilies, which are tabulated below.
Two courses are open in making a key to the sub- families. In both Isoperla and Alloperia the forking of the cubitus in fore-wings is such that the upper branch of cubitus goes out straight as a continuation of the stem, while the lower branch (cubital fork) plainly diverges from the stem and upper branch of cubitus. In all other Perlidae the forking of cubitus is so that the upper branch diverges from the stem, plainly at least a little. But the Isoperlinas and the Chloroperlinae (Alloperia) differ in so many ways, and, as I believe, the Isoperlinse are an off- shoot of the Isogeninae that I think it better to take out the Chloroperlinae much before the Isoperlinae. Another matter permits of two solutions. Whether to
put together all those forms which have femoral bristles, or to dispose of them according to the forking of the



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19471 Banks-Characters in the Perlida 275 cubitus; I have chosen the latter course. Bristles are
ancestral, and the occurrence of ancestral characters in descendants is not unusual.
I had started this paper in order to do identification, especially of New England Perlidae, and had hoped to rely chiefly on body characters, but find (as others have) that there is much in the wing, particularly the basal portion that is sufficiently constant for synoptic purposes. I do
not underrate male genitalia and am pleased to find that in general my results agree with the plan made by Richer in 1943.
1. Head longer than broad, eyes situate more than twice their diameter from hind margin; in the forking of cubitus the upper branch is bent a little from the stem; the third anal vein arises from the cell; no anal lobe nor anal brace ; antennse with a few joints near base short; a carina or line connecting eyes and passing just behind hind ocelli.
Kathroperlinse
If head is longer tha,n broad the eyes are not more than one and one-half diameter from the hind ............................................................................................................... margin 2 2. Small forms less than an inch; no anal lobe nor brace; anal area of hind wings with not more than four longitudinal veins ; distinct erect bristles in a row on each side of femoral groove; occipital line absent or indistinct; antennae rather long, not thickened at base, the joints monilif orm ; usually in the fore wings the third anal vein branches from ............
the second beyond the anal cell
Chloroperlinse
Anal area of hind wings with more than four longi- tudinal veins ; in the fore wings the third anal vein leaves the second at or before end of anal cell ...... 3 3. But two ocelli ................................................................................................ 4 With three ocelli .......................................................................................... 6 4. Head about twice as broad as long, partly under the overhanging pronotum, latter very broad, rounded behind, straight or slightly concave in front; legs



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276 Psyche [DW.
short; setae very short, but basal joints distinct; costal cross-veins numerous ...................... Peltoperlinae Head usually longer; pronotum usually a little con- ........................ vex in front; setae not especially short 5
5. Ocelli hardly three diameters apart; anal brace dis- tinct, extending obliquely back; femora with bristles among the hairs, no cross-veins between first and second anal veins .............................. Neoperlinae Ocelli fully four diameters apart ; anal brace faint or absent, usually a few cross-veins between first and second anal veins ............ Atoperia in Perlestinae 6. In fore-wings there is an obliquely recurrent anal brace, often arising near base of third anal vein.