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XIV. On Diopsis, a Genus of Dipterous Insects, with Descriptions of Twenty- 

 one Species. By J. O. Westwood, Esq., F.L.S. 



Head November 5th, 1833; and November 4th, 1834. 



The immortal man whose name ve, as a body, have adopted as our own, 

 terminated his zoological labours by the publication of the " Dissertatio Ento- 

 mologica, bigas insectorum sistens," scil. Paussus and Diopsis, as though, to 

 use the \tords of his countryman Dalman, " Linnaeo hoc, lit videtur, erat con- 

 silium, ut vellet absolvere illustrem suum cursum entomologicum per pro- 

 ductum quoddam insigniter singulare, vix quidquam magis singulare ex- 

 cogitari potuit quam Paussus et Diopsis." 



Of the former of these two genera, in its present state, as a family, I have 

 given a detailed account, which the Linnean Society has done me the honour 

 to publish in the 16th volume of its Transactions. In order to show in some 

 degree my sense of this honour, I have taken up the latter genus, and I now 

 beg to offer to the Society the present memoir as a fitting companion to my 

 former communication ; moreover, the now prophetic, but, at the time, erro- 

 neous reference by lUiger to the Linnean Transactions for a memoir upon this 

 genus, had a second-rate influence in this choice of subject. 



The CHIEF INTEREST of the genus Diopsis arises from the extraordinary elon- 

 gation of the sides of the head into two cylindrical horns, which in some in- 

 stances are as long as the whole body, and at the extremity of which the eyes, 

 of a semi-globular form, are placed : the antennae also are inserted near the 

 extremity of these protuberances at a short distance before the eyes. At first 

 sight these horns might easily be mistaken for antennae ; but they are inarticu- 

 lated at the base as well as along the surface ; they have, therefore, no inde- 

 pendent motion, their movements being necessarily accompanied by those of 

 the whole head : when, however, we recollect that they contain not only the 

 infinity of nerves of the compound eyes at their extremities, but also those 



VOL. XVII. 2 p 



