64 G APPENDIX. 



Vol. ii. p. 308. Genus STOASTOMA. 



Mr. Chitty has described a new genus, under the name of 

 Lewisia, to include those species of Stoastoma in which the 

 shells are as it were double-mouthed. 



Genus LEWISIA, Chitty. 



Shell sub-discoidal ; aperture semi-ovate ; peristome con- 

 tinuous, with a spiral callus at the base excessively developed, 

 usually soldered by its extreme edge to the last whorl, and form- 

 ing over the umbilicus an arch, having the opening larger than 

 the aperture of the shell. 



Ex. L. Philippiana, C. B. Adams, pi. 138, fig. 12, 12, a. 



S. Agassizianum, and two new species described by Mr. Chitty, 

 also from Jamaica, belong to this group. 



Mr. Chitty has further proposed six other genera, which may 

 be considered as sub-genera of Stoastoma. The genus Stoa- 

 stoma, as restricted, will then comprise S. Pisum, Pfeifferianum, 

 and a third species described by Mr. Chitty. The new sub- 

 genera are as follows. 



Sub-gen. wilkinson^ea, Chitty. 



Shell sub-discoidal, spirally carinated, last whorl much pro- 

 duced. 



This division will include S. Goiddianum, Hollandianum, 

 Tappanianum, Wilkinsonia;, and nine new species described by 

 Mr. Chitty. 



Sub-gen. fadyenia, Chitty. 



Shell with the spire depressed, sub-angular on the upper 

 part of the last whorl, sub-planate at the periphery, sub-angulated 

 below, and sub-planate round the umbilicus. 



Of this group S. Fadyenianum is an example, and Mr. Chitty 

 has described two other species. 



Sub-gen. metcalfeia, Chitty. 

 Shell depressed, conic. 



