378 Mr. W. H. Benson on the genus Tomichia. 



? Truncatella, Risso. 



"Operculum membranaceuni, obsolete spiratum. Testa (junionim 

 turrito-snbulata) adulta cylind.ica, truneata, Apertura oblongo- 

 ovalis. Peiistoraa simplex vel duplicatum, marginibus distantibus, 

 callo junctis." 



T. ventricosct, tlie 14th species, is there included with a (?) 

 prefixed. This fornix the shell of which, examined apart fi-om the 

 animal, exhibited to Dr. Pfeiffer safficient ground for ascribing it 

 with hesitation to Risso's genus, I now propose to separate from 

 that group on account of the peculiar characters observed in the 

 living animal. Having, immediately on my first discoveiy of live 

 examples, in October 1846, separated the genus, in my journal, 

 under the designation here adopted, with regard solely to the 

 characters of the iiihabidng mollusk, it is satisfactory to be able 

 thus to confirm the suspicioiis suggested to a learned concho- 

 logist, and skilful describer, by the mere inspection of the testa- 

 ceous covering. 



Tomichia, nobis, nov. gen. 



Testa perforata, spira elongata ; anfractibus sabsenis ; apice plerum- 

 que truncato. xlpertuva oblique elliptico-ovali, verticali; peristomate 

 duplicato vel triplicato, continuo, margiiie siuistro expanso, reflex- 

 iusculo, leviter emarginato ; epidermide olivacea. 



Animal. 



Proboscis elongata, transverse corrugata, ad apicem emarginata. Ten- 

 tacula duo mediocria, filiformia, ad apicem obtusa ; oculis postice, 

 prope basin superiorem tentaculcirum, insaper tubercula, positis. 

 Pes brevis, ovatus, antice ad latera utrinque lobatus, postice lobo 

 dorsali, operculum gerente, prseditus. Operculum * corneum, sub- 

 spirale, anfractibus velocissime crescentibus, nucleo sub-basali, ad 

 latus sinistrum posito. 



* The operculum is very similar in structure to that of the Gangetic Assi- 

 minia {Turbo) Francesia, Gray. Several of the continental conchologists 

 appear to be unaware of the peculiar characters of Assiminia, as given, in 

 1834, by the Rev. Mr. Berkeley in page 429, from the English ; and by 

 myself in page 463 of the 5th vol. ' Zoological Journal,' from the Indian 

 species. Dr. Philippi (Ahbild. t. 1. f. 15) refers A. Francesix, Gray, to 

 Paludina, remarking (tab. 2. f. 6) that the Brazilian P. atomaria may pos- 

 sibly be an Assiminia ; but that he did not know any distinguishing cha- 

 racter between the genera. Now the presence of a subspiral, in contradi- 

 stinction to a concentrically laminar operculum, independently of the posi- 

 tion of the eyes at the summits of the two tentacida, alone suffices to pre- 

 vent the fusion of the two genera ; characters for separation are not, how- 

 ever, wanting in the shell, if regard be had to the invariably discontinuous 

 peristome, to the more regularly conical spire with flattened whorls, and to 

 the acutely pointed apex, which, even in the absence of the operculum and 

 animal, permit of the recognition of a specimen of Assiminia. 



