Mr. F. W. Edwards 07i Lyglstorrbiiia uriclii. 203 



N.B. — The copulatory hooks of the male give very good 

 specific cliaracters in this genus, and many of them have 

 been figured by Reuter in various papers and by Champion 

 in the ' Biologia Centrali-Aniericana/ Tht-y are often fairly 

 well visible from the side of the abdomen ; but in some 

 species, as in the above-described corixipennis^ they are of a 

 rather complicated structure and must be detached from the 

 body (whicii can be easily done without injuring the abdo- 

 men) and examined from different sides. 



XXT. — Lygistorrhina urichi, a new Miicetophllid from 

 Trinidad. By F. W. Edwards, B.A., F.E.S. 



(Published by permission of the Trustees of the British Museum.) 



The writer has received for examination from Mr. H. Scott, 

 of Cambridge, a small series of a very peculiar and interesting 

 ]\rycetophilid, described below. Tlio species is undoubtedly 

 congeneric with Williston's Probolceus singularis from 

 St. Vincent, but, for reasons which will appear, the writer 

 does not consider that Probolceus can be retained as a distinct 

 genus from Skuse's Lygistorrhina. The latter was described 

 (in the female sex only) as possessing three ocelli, the median 

 one being minute. In Frobokeus (described from males 

 only) the ocelli Avere described as apparently absent, the 

 remaining characters of P. singularis being almost exactly 

 like those of L. insignis. Fortunately in Mr. Scott^s series 

 both sexes are represented, and a careful examination showed 

 that while in the male ocelli seem to be absent, in the female 

 a pair of large ones is present in the same position as in 

 Lygistorrhina. The loss of the ocelli in the male is no doubt 

 due to the much greater development of the eyes, which are 

 quite twice the size of those of the female. The chief 

 (supposed) distinction between these two genera is thus 

 proved to be non-existent, and Probolceus therefore becomes 

 a synonym of Lygistorrliina. There are, however, some 

 slight differences which can hardly be considered of generic 

 value: (1) In L. urichi the median ocellus is apparently 

 wanting; (2) in the two West-Indian species the mediastinal 

 vein (sc) reaches the costa, while in the Australian L. insignis 

 it does not ; (3) Lygistorrhina has two small spurs to the 

 middle tibiee, Probolceus only one. 



