F. M. Hull.
An Interesting Oceanic Species of Cerioides (Diptera; Syrphidae).
Psyche 54:181-182, 1947.

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AN INTERESTING OCEANIC SPECIES OF
CERIOIDES (DIPTERA; SYRPHID^E)l
BY F. M. HULL
University of Mississippi
I am indebted to Dr. Joseph Bequaert, Curator of In- sects at the Museum of Comparative Zoology, for calling my attention to the following interesting species of Cerioides.
Cerioides (Tenthredomyia) williamsi n. sp. Related to oceanica Hull; differing in the pattern of the yellow markings.
Male. Length about 16 mm., including the down- flexed abdomen, and including antennae (2 mm.) . Head: vertex and front shining black and almost bare. Upon the front there is on either side a sunken, hemicircular, opaque black pubescent, eye marginal area ; at the upper end of this area there is a small patch of brownish-white pubescence. The face is dully shining black, with a sharp, wide, pale, yellow stripe on either side ; this stripe margins the eyes on the upper half to the upper limits of the antenna1 pedicel, and below the stripe narrows as it is directed along the anterior, black cheek margins to the epistoma which it just fails to reach. The antennae are entirely velvet black; the first segment is barely longer than the third, the third a trifle longer than the second; the pedicel is about as long as the second seg- ment. Thorax: brilliant shining black with large, bright, pale yellow spots. These spots consist of the humeri, a spot on each side at the lateral end of the transverse suture (notopleural), a vertical spot covering- most of the mesopleura, and all the scutellum except for a black, round, middle portion, which does not quite reach its posterior margin. Abdomen: broad at base, but little constricted, everywhere shining black, and with faint blue-purple luster apically. The narrow posterior mar- 1Published by a grant from the Museum of Comparative Zoology at Harvard College.
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182 Psyche 1 Sept.
gin of the second segment, and still more narrow margin of the third segment is pale yellow. The abdomen is strongly flexed downward beginning with the third seg- ment, its extremely short, everywhere wholly appressed pile is white except broadly over the middle of the second segment where it is black. There is a small, lateral yel- low spot on the sides of the first segment, scarcely dis- cernible from above. Legs: blackish brown, nearly the basal half of all tibiae whitish. All pile white; femoral setae black, very sharp pointed. Wings: hyaline, the an- terior border as far as the spurious vein very dark sepia brown, without evident lighter areas, even in the costal cell. Loop of third vein very shallow, and with a short spur.
Holotype: a male, Noumea, New Caledonia, October 16,1940 (F. X. Williams). Paratypes: 2 males, La Foa, New Caledonia (C. L. Remington). Holotype in the Museum of Comparative Zoology (No. 27559). There is a paratype in the collection of the author and another in the Museum of Comparative Zoology.
Dr. Bequaert has kindly called my attention to the wasp which mimics this fly.
The wasp model is Pachy-
menes quodi Vachall, a Eumenid. Mr. Williams, in the Proceedings of the Hawaiian Entomological Society, 1945, Vol. XII, plate xx, illustrates the fly and the wasp and calls attention to other mimics.




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