a Genus of Dipterous Insects. 289 
(mento?) brevi, cylindrico, apice vel capitulo carnoso, compresso, bilo- 
bato, corrugato, tenuitér pubescenti. Truncus elongatus, subovatus, anticé 
attenuatus, mesothorace interdim, scutello metathoraceque semper utrin- 
que unispinosis, hoc distincto, subquadrato. Halteres nudi. Ale ut in 
Calobatd reticulate, nervo angulari basali interno nullo. Pedes elongati, 
antici raptorii coxis longis, femoribus plùs minüsve incrassatis, et subtüs 
serie duplici denticulationum parvarum instructis, tibiis subarcuatis. Fe- 
mora 4 postica gracilia, ad apicem interdüm unispinosa. Tibic postice 
inermes, recte. Tarsi 5-articulati, articulo Imo longissimo.  Pulvilli 
magni. Abdomen elongatum, angustum, plùs minüsve clavatum, ad basin 
attenuatum, suprà convexum, subtüs tamen concavum, segmentis 4 anticis 
arcté conjunctis, haud articulatis, ad basin suprà subcanaliculatum. 
The differentice sexuales in this genus have not hitherto been clearly ascer- 
tained. Dalman says, “Abdomen maris lineare, feminz pone medium in- 
adding, “ Ob formam abdominis in una eademque 
, 
crassatum, subclavatum ;’ 
specie diversam, linearem nempe vel clavatam, illam maris, hanc feminze sexum 
indicare, suspicari liceat.” Dalman, however, had observed this variation in 
one species only, D.signata. From the differences, however, existing in spe- 
cimens of D. fasciata, D. assimilis, and D. Sykesii, it would seem that the cla- 
vation of the abdomen is not confined to the female; whilst it also appears 
that in some species the males are distinguished by the greater length of the 
ocular peduncles: that this, however, is not always the case is evident from 
these organs not being longer in the slender specimens of D. signata, fasciata, 
and assimilis, than they are in the more robust ones. I observed, moreover, 
in the robust specimens of D. Sykesii, as well as in D. fasciata, a minute 
exserted style at the extremity of the last (incurved) segment of the abdomen : 
hence, taking the characters of all the species into consideration, it appears 
that the females are larger and more robust than the males, their abdomens 
more distinctly clavate, whilst the ocular peduncles of the males are more 
slender and often longer than those of the opposite sex*. 
* The celebrated Danish traveller and naturalist M. Lund informed me that the males alone in 
Diopsis possess the elongated processes of the head; but it is evident that he referred to the insects 
which he had collected in Brazil, and which Wiedemann has described under the name of Zygothrica 
dispar. 
