154 Proceedings of the Royal Society of Victoria. 



possession examples of these opercula, varying from one-sixteenth 

 to one and a quarter inch in diameter, and from one-fiftieth to a 

 quarter of an inch in thickness, thus establishing the fact that 

 they are both larger and smaller than the measurements 

 previously given by me. He also informs me that in the collec- 

 tion 6f the Rev. Mr. Cresswell is a specimen of Oriostoma Northi 

 with a similar operculum in situ., the shell about two and a half 

 inches in diameter, and the operculum three quarters of an inch. 

 Mr. Pritchard obtained a broken mouth of an Oriostoma at Lily- 

 dale, about live or six years ago, also with the operculum in its 

 natural position. This was submitted to Professor Sir P. McCoy, 

 and its nature deterujined by my eminent friend, who referred 

 the fragment to Euomphalus. We have here the explanation of 

 Mr. Hall's reference to the latter. 



Mr. Pritchard's smallest O. JVoj-thi, a perfect young example, 

 is half an inch in diameter, and yet is too large for the smallest 

 of the operculums in his collection, whilst the largest specimen of 

 this species is three and a quarter inches in diameter, with the 

 operculum one inch in the same direction, so that the largest of 

 the "lids" mentioned above (one and a quarter inches), seemingly 

 indicates a very large example of the species. 



These observations of Mr. Pritchard's will, I think, fairly 

 answer my previous question as to which of the Lilydale shells 

 our button-shaped bodies belong to. Furthermore, this additional 

 evidence opens up the question — How far can the depressed 

 Euomphaloid shells referred to Oriostoma, such as my O. N'orthi, 

 and other similar forms, be properly placed in Oriostoma ? Can 

 they, with their amphicoelean opercula, be relegated to the same 

 genus as those species so beautifully figured by Dr. Lindstrom, 

 and touched on by Mr. Smithe and myself, with more or less 

 conical opei'cula ? It is a rather significant fact that all 

 Lindstrom's figures showing opercula in situ, represent species 

 with the more elevated &pire, after the type of O. discors, Sby., 

 O. globosum, Schl., and its var. sculptum, Sby., and not those with 

 a depressed spire such as O. rugosum, Sby., nor those with a 

 concealed spire (in a side view), like O. augulatiim, Wahl. 

 However, the subject is too long and complex to be considered 

 now, and I hope at no distant date to communicate a paper to 

 the Royal Society on the subject, and on the general family 



