of mollusca. 83 



21. Otopoma. 



Operculum shelly, solid ; whorls convex in the centre, with simple 

 edges. Shell conically subglobose or depressed ; aperture subovate. 

 Peristome straight or slightly expanded, with the columellar margin 

 for the most part dilated, covering part of the axis, or closing the 

 umbilicus. 



1. 0. Listeri, t. 311. f. 10. 



22. Cyclostomus. 



Operculum rather ovate, shelly, flat ; whorls four to five, gradually 

 increasing, with simple margins ; nucleus excentric. Shell depressed, 

 globose-turbinate or ovate- turrited ; aperture ovate. Peristome 

 simple, straight or expanded, often double. 



1. C. elegans, t. 293. f. 1, t. 311. f. 5?, 9?, 14, 16, 17. 



2. C. novae hiberniae, t. 311. f. 13. 



Fig. 47. — Cyclostomus elegans. 



23. Tudora. 



Operculum ovate, shelly, flat, of few whorls, which are enlarged 

 rapidly and arcuately grooved or deeply striated obliquely, with the 

 nucleus very excentrical. Shell ovate-oblong or turrited ; aperture 

 angularly ovate. Peristome expanded, simple or double. 



1. T. ferruginea. 



24. Leonia. 



Operculum ovate, shelly, very convex externally, with a single 

 whorl and the nucleus situated near the columellar margin. Shell 

 ovate-conical ; aperture ovate. Peristome simple, slightly reflexed. 



1. L. mamillaris. 



25. ClSTULA. 



Operculum ovate, thin, cartilaginous, with a thin external shelly 

 coat with few gradually increasing whorls, the margin of which is 

 usually detached ; nucleus excentrical. Shell globose-conic or ovate, 

 or oblong-turrited, usually truncate ; aperture ovate. Peristome 

 simple, expanded or double. 



1. C. catenata. 



b. Operculum thin, horny ; last whorl rounded in front. 



26. Chondropoma. 



Operculum ovate, subcartilaginous, flat ; whorls few, rapidly in- 



g 2 



