162 



me for a group of shells of which the Gyp. edentula, Gray, is the 

 only example at present known. 



With regard to Erato, although its animal possesses much in 

 common with that of Trivia, particularly in the dentition (if cor- 

 rectly figured), yet I agree with Mr. Tryon that " the balance of 

 characters seems to indicate a rather closer relationship " with 

 Marginella, where he has placed it. At any rate, the genus is 

 already monographed in this work, vol. v, p. 1. 



Besides these, the following fossil genera have been estab- 

 lished : Cypraeorbis and Sulcocyprsea, named by Conrad, but not 

 described, and Cyprsedia, Swainson. Pseudocassis, Pictet, erro- 

 neously referred as a synonym to Gaskoinia, Roberts, in Try on 's 

 Structural and S} r stematic Conchology, scarcely belongs to the 

 family. 



The following arrangement is suggested after careful study as 

 being that best attainable by me, but on account of the great 

 variability of form and other characters. I am convinced that no 

 scheme of classification can be presented that will positively 

 determine the position of all the species. In using the sub- 

 generic terms here given, I do not recognize in them any syste- 

 matic value except in the case of Trivia, which is sufficiently 

 well characterized to entitle it to the position of a subgenus. 



Genus CYPRJ3A, Linn. 



Section I. Shell cylindrical, or nearly so. 

 Group A. Not margined. 



* Spotted, teeth brown-tinted. 

 ** Not spotted, teeth whitish. 



Group B. Margined. 



* Margins not spotted. 



** Margins spotted, teeth small. 

 Section II. (Aricia, Gray, pars.) 



Shell ovate, thick, margined with flattened base. 

 Group A. Shell smooth. 



* Not spotted. 



** Dorsal surface spotted. 

 ^*^ Spots extending over the base. 

 Group B. Shell sometimes nodose or tuberculated. 



