THE NAUTILUS. 89 



lighter columellar callus. It is easily distinguished from other 

 described species by its size. 



Clappia, n. gen. 



Shell small, globose-turbinate, narrowly, but deeper umhiUcate, 

 aperture large, lip simple, columellar lip simple, adiiate to body- 

 whorl only at the extreme upper portion, oblif|ue, expanded and 

 subangulale to iis union with the basal lip, operculum corneus, 

 paucispiral, nuclear whorls large and subcircular, slowly and grad- 

 ually increasing. 



Rachidian tooth of the radula short and broad ; intermediate tooth 

 with sub-quadrate body with a strong tooth projecting from the in- 

 fero-anterior angle and a large peduncle; laterals multicuspid: 



Formula of the denticles : ^~^~^ 10-1-10, 50+, 50-1- (Fig. 7). 



Type : Clappia clappi Walker. 



This genus stands close to Somatogyrus, but differs in several im- 

 portant particulars, which forbid the reference of the type species to 

 that group. 



The central tooth of the radula is very similar both in shape and 

 in the arrangement and number of the denticles to that of S. de- 

 pressus as figured by Stimpson. But the intermediate tooth lacks 

 the perforation, which is found in that species, and has a prominent 

 tooth at the infero-anterior angle which is lacking in the other. The 

 laterals are multicuspid. In this respect, Clappia stands in the same 

 relation to Somatogyrus that Cincinnatia does to Amnicola. 



In shell characters, Clappia differs from Somatogyrus in the con- 

 spicuous deep umbilicus, the straight, thin inner lip without any 

 callus thickening, which is entirely separate from the body whorl, 

 except for a very short distance at the upper extremity. 



The operculum is also very different. In all the species of Soma- 

 togyrus examined, the nuclear whorls of the operculum are very 

 small, while the last is enormously expanded (see Fig. 6, .S'. subgloh- 

 osus, Fig. 5, S. depressus). In Clappia (Fig. 4), on the other hand, 

 the nuclear whorls are large and nearly circular, and form nearly one- 

 half of the whole operculum. Indeed, in looking at the operculum in 

 situ, the first impression is that it is completely circular as in Valvata. 



Clappia clappi n. sp. PI. vi, figs. 1, 4 and 7. 



Shell small, globose-turbinate, narrowly and deeply umbilicate ; 



