of some new Species of Mydasida. 91 



colour, the posterior femora but slightly clavate and serrated 

 beneath. The wings are quite limpid, with the veins very slightly 

 tinged with brown. The veins are arranged as is described in the 

 last species. The abdomen is terminated by a retractile ap- 

 pendage, armed with a radiating series of pale-coloured setae. 



XXV. Descriptions of some new Exotic Species of Acroce- 

 ridae (Vesiculosa, Latr.), a Family of Dipterous Insects, 

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



[Read January 3, 1848.] 



The family, whereof I propose in the present paper to describe a 

 number of new species, is remarkable for the singvdarly swollen 

 body, and more particularly abdomen, of nearly all the species, 

 whence Latreille gave to the group the sectional name of Vesicu- 

 losa. This peculiarity does not exist alone in this family of 

 insects, since we meet with various analogous resemblances in 

 other orders of insects, and indeed in other tribes of animals. 

 Among the Coleoptera there is the genus Chactas amongst the 

 Melyridce, and some Heteromerous genera, remarkable for their 

 very swollen elytra. Amongst the Homopiera there is also a 

 very remarkable genus of Cicadidce from New Holland, figured 

 by me, in the "Arcana Entomologica," under the name of Cystosoma 

 Saundersii. There are also some Orthopterous genera, and many 

 Homopterous, in which the scutellum is dilated and swollen, con- 

 cealing the wings and abdomen ; as well as some Crustacea, such 

 as the crab-genus Hymenosoma, and some fishes, which are similarly 

 swollen. 



The naturalist will do well not to overlook these kinds of 

 analogies, and they require to be stored up for future use. To 

 attempt in the present state of science to apply them fully and 

 fitly is a vain effort of skill. 



Of the singular family Acroceridce I believe nothing is still 

 known of their habits ; the species are everywhere very scarce, 

 and no observation has hitherto been made of their transforma- 

 tions. The genera are but few in number, but the species are 

 distributed over the greater portion of the globe. I do not how- 

 ever remember any Asiatic species, although African, Australian, 



