248 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



R. aurata, and the smooth whorls with diagonal lines of color in 

 R. nana are the most constant distinction. 



R. melanostoma is marked with R. aurata by Gray floe. cit.J as 

 variety of one species. This I believe. At any rate, the former 

 is unknown to me. It is the oldest name, but from the imperfect 

 diagnosis of Chemnitz it is impossible to identify the shell meant 

 as a Jtisella. 



R. plana, Quoy, is a very depressed solid angular Urate and 

 plicate species with a yellowish white mouth. It is longer than 

 the preceding, and its specific characters seem very constant. The 

 animal I have not seen. The shell is found all round the Aus- 

 tralian coast from Port Stephens to S. Vincent's Gulf. 



R. lutea, Quoy, I believe to be only a corroded and brackish 

 water or male variety of the preceding ; but I know little of 

 the living habits of the species. In Dr. Cox's extensive collec- 

 tion, I noticed the shells named R. lutea which appeared to me a 

 common form of R. nana or aurata, but adult or perhaps 

 more correctly in old age. It is corroded, and the mai'ginal 

 space on the base is not visible. It is common in Tasmania, 

 and breeds readily with R. nana. Mr. Angas says (Zool. 

 Proc. 1867, p. 209), this species, the most conical of the 

 genus, is common on the rocks outside Port Jackson, and along 

 the coast to Kiama and Jervis Bay. Mr. Crosse (loc. cit, p. 238) 

 says, on the authority of MM. Q. and G., that it is found through- 

 out King George's Sound, but principally in the little salt ci'eeks. 

 The only good figures, says M. Grosse, are those of Kiener, in his 

 monograph of the genus Trochus — but there is no description as 

 the work is not completed. 



Thus we should have only two species of Risella, with male or 

 female varieties of both. 



It is possible that these two species may even yet be reduced to 

 one ; but I respectfully beg the attention of naturalists to the fact 

 that the sexual differences are marked by differences in the shells. 

 This may open up a most important, fact for the whole of our con- 

 chologic d nomenclature. I also call attention to the remarkable 



