98 ASSIMINEID^. 



Clark succeed in detecting any branchiae, although he 

 has given us the number of strands in the gill-plume 

 of Aclis unica, which in bulk is only one- tenth of A. 

 Gray ana. According to Mr. Blanford, Dr. Leith de- 

 scribed some species of the present genus, under the 

 name of Optediceros, in the ' Journal of the Bombay 

 Branch of the Royal Asiatic Society ' for 1853, one of 

 his generic characters being as follows : — " The respira- 

 tory opening is a round perforation in the mantle, be- 

 hind the right tentacle." I have observed the air-pouch 

 of A. Grayana and A. littorina ; in the latter it is very 

 conspicuous and unmistakable. The shell of A. Gray- 

 ana is not unlike that of a young Limnaa palustris, 

 especially of its variety conica ; and as both belong to the 

 same order, and I was not then aware that Assiminea 

 has an operculum, my error in following Dr. Fleming, 

 who placed A. Grayana in the genus Limncea, was per- 

 haps not so heinous as Dr. Gray made it out to be. 

 Against this criticism of the last-named author may be 

 set off a remark that there is no foundation for his 

 statement that the eyes in A. Grayana " are placed on 

 a peduncle as long as the tentacula, and the peduncle 

 and tentacula are soldered together." The eyes are 

 imbedded in the tissue of the tentacles ; and there is no 

 peduncle or stalk. The dental apparatus is somewhat 

 complicated, each row consisting of a central tooth 

 flanked on either side by three uncini of different 

 shapes. 



This genus bears also Gray's MS. name of Nerita 

 Syncera, and has been called Assiminia and Assaminia. 

 With respect to the present name the author ought to 

 have borne in mind one of Linnets laws of scientific 

 nomenclature, " Idiotae imposuere nomina absurda." 

 Woodward was clearly mistaken in considering it a 



