284 Mr. Westwoop on Diopsis, 
producing the sensation of which the antenne are the seat, we can easily 
imagine how necessary it is that the means of communication with the re- 
mainder of the head should be unbroken by articulations. 
Linnzeus observes that this genus, on account of these ocular peduncles, is 
distinguished “non a Dipteris solum, sed ab omnibus etiam insectis huc 
usque mihi cognitis.” Since his day, however, other insects have been dis- 
covered presenting a somewhat similar formation: of these, the Dipterous 
genus Achias, Fabr., is nearly allied to Diopsis, and of this M. Guérin has given 
an account, illustrated by very good figures, in the first number of his “ Maga- 
sin d’ Entomologie,’ drawn from the original unique specimen described by 
Fabricius from the cabinet of M. Bosc, which, I am sorry to say, had suffered 
materially from the ravages of insects when I inspected it at the Jardin des 
Plantes*. From M. Guérin’s figure it is evident, however, that the eyes only 
in Achias are fixed at the extremity of the peduncles, the antenne being 
inserted in the middle of the face: the same remark is also applicable to 
several other insects with long ocular peduncles, which were at first described 
by Wiedemann as belonging to the genus Achias, but subsequently formed by 
him, in a memoir read at the meeting of German Naturalists in 1830, into 
distinct genera, namely, the Plagiocephalus lobularis and Zygothrica dispar, 
both brought from Brazil by M. Lund; to the latter of which (at least to the 
female) is also allied the Trigonosoma perilampiformis of Gray (Griff. Anim. 
Kingd., pl. 128.). In like manner the different species of the SrREPSIPTEROUS 
genera Xenos and Stylops, as also the recently established genus Halictophagus, 
Curt., have the eyes placed upon very short footstalks. The genus Elenchus, 
Curt., however, belonging to the same order, does not appear to be so circum- 
stanced, since Robert Templeton, Esq., who has written and kindly presented 
to me an account of this genus illustrated by figures, states that the eyes are 
sessile. Certain male Ephemere are also remarkable for having a supple- 
mental pair of eyes placed upon short peduncles between the lateral eyes. 
In the order Hemiprera (Heteroptera) De Geer has also figured three spe- 
* The existence of this remarkable genus fortunately does not rest upon this single mutilated spe- 
cimen, since Dr. Horsfield has been kind enough to show me a specimen of a distinct and very beautiful 
species with maculateá wings, captured by himself in Java; and amongst the unascertained species 
at the East India House I noticed the female of this new species, in which sex the head is not broader 
than the thorax. 
