a Genus of Dipterous Insects. 291 
cludes it from his * familia Achitdarium,” probably on account of the form 
and position of its antennz. Latreille also, in the second edition of the Règne 
Animal, removes it from Achias, and places it amongst his Carpomyze, im- 
mediately after Calobata, and before Cephalia, Sepsis, Ortalis, &c. With these 
genera, indeed, it appears the most nearly allied, not only in the elongate form 
of the body, but also in the maculation of the wings. The structure of the 
mouth, however, in Diopsis, previously described, seems to indicate the want 
of a decided affinity with these groups. 
Hitherto no facts respecting the habits of this genus have been published. 
Dalman, evidently speaking from information supplied to him by Afzelius, 
states that the latter found his specimens merely by accident in the windows 
of houses. He has, however, made two observations, which are sufficient of 
themselves to prove him to have been a first-rate entomologist, rendering 
our regret at his loss the more painful: *Insectorum oculos valde promi- 
nentes semper fere vitam super sabula vel ad ripas indicare, ut colligere licet 
ex Cicindela, Elaphro, Omophrone, Steno, inter Coleoptera; Salda, Alydo inter 
Hemiptera. Ceterum oculorum prominentia preesertim insectis rapacibus 
videtur esse propria, et adaptata ad istum vivendi modum, ut in jam supra re- 
censitis et in Libellulinis, Hemerobio et aliis ;" adding, however, * Oris tamen 
ratio in Diopsi a preeda capienda aliena videtur." The statement, however, 
which Colonel Sykes has been kind enough to furnish me with respecting the 
habits of D. Sykesii, subsequently detailed, prove that in regard to this genus 
Dalman was correct in his supposition that insects with prominent eyes affected 
moist situations, whilst the raptorial fore legs and the more developed structure 
of the mouth show that his latter observation cannot be far from correct. 
As to the characters which constitute the specific distinctions observable in 
the following insects, it is to be noticed, that from an examination of not less 
than thirty-five specimens of D. Sykesii, variation in colour appears to be of 
the first importance in this group. It will be seen, however, from Dalman's 
observation upon D. signata, that even colour is liable to variation, although 
evidently only to a slight extent. Scarcely the slightest variation in this respect 
existed in any of the specimens of D. Sykesii. The length of the horns, which 
Dalman gives as one of the leading characters of his D. macrophthalma, is, as 
stated above, a sexual difference, and therefore ought not to be employed. 
VOL. XVII. 2Q 
