68 ANNALS NEW YORK ACADEMY OF SCIENCES 



Potamidopsis tricarinata mut. baucis mut. nov. 



1804. Cerithium tricarinatum var. /3 Lamarck, Ann. du Mus. Nat. d'hist nat- 

 urelle, Paris, III, 272. 



The author says of this species : 



Dans la variete j3, la car^ne superieur de chaque tour est un peii plus 6mi- 

 nente que celle du milieu. 



The mutation is apparently more common than the type species, since 

 it is rare to find specimens in which the two upper rows of nodes are 

 equal. The upper row is slightly stronger, even in the type figured in 

 Paleontologia Universalis, but the varietal name may be retained for 

 those forms in which the difference is strongly developed. 



No. 20121, Columbia University collection. 



Potamidopsis tricarinata mut. brontes mut. nov. 



1824. Cerithium tricarinatum var. b Deshayes, Desc. des coquilles foss. des 

 environs de Paris, II, 325, pi. 51, fig. 2. 



This mutation is distinguished by the strong carina which forms a 

 projecting shelf around the whorls and by the fine nodes of the two upper 

 spirals. The shells of this variety are usually larger than those of the 

 typical form. 



No. 20123, Columbia University collection. 



Potamidopsis tricarinata mut. cronus mut. nov. 



1824. Cerithium tricarinatum var. c Deshayes, Desc. des coquilles foss. des 

 environs de Paris, II, p. 325, pi. 51, figs. 3, 4. 



The carina of this mutation is also very strong, but the nodes are more 

 widely spaced and more prominent than in the mutation hrontes. The 

 median row of nodes is obsolete and the upper row is poorly developed. 



Potamidopsis tricarinata mut. doris mut. nov. 



1824. Cerithium tricarinatxtm var. d Deshayes, Desc. des. coquilles foss. des 

 environs de Paris, II, p. 326, pi. 51, fig. 6. 



This mutation is similar to the last, but in this form it is the siib- 

 sutural row of nodes which becomes obsolete. 



