INVERTEBRATE PALEONTOLOGY. 555 



II. and A. Adams have divided the recent species of this genus into the 

 follow iiiy two subgenera: 



1. columna, Perry (rr Acicula, Blainv.). 



Shell sinistral, with volutions generally convex, last turn not 

 angular or excavated below. — (Type as already cited.) 



2. rhodea, H. and A. Adams. 



Shell dextral, very slender and elongate-cylindrical ; last turn 

 flattened, carinated below the middle, and excavated below the carina; 

 columella thickened, and subtruncated at the base. — (C. Califomica, 

 Pfeiffer.) 



These two sections, looking at the recent species only, would seem to 

 present sufficiently well-marked differences to rank as distinct genera. 

 When we come to compare some of the intermediate extinct species, how- 

 ever, such as C. columnella, Deshayes (sp.), and C. Rillyensis, Boissy (sp.), 

 from the Paris-basin Tertiary, in which forms the lower volutions are flat- 

 tened, and the last one subangular below, the Rhodea group will be seen to 

 be less strongly separated from the typical form of the genus than would 

 appear from a mere comparison of the living species only. 



Unless the following-described species may belong to the upper beds 



of the Cretaceous, this genus would seem to have been introduced during the 



Eocene epoch. The three living typical species are found on Prince's Isle, 



west coast of Africa, and another in Madagascar. The type of the section 



Rhodea occurs in California, and was described by Pfeiffer under the name 



Achatina Califomica. 



C o I ii in ii a teres, M. & H. 



Plate 44, figs. 11, a, b. 



Bulimus ? teres, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 117 (not B. teres, Oliv., 



Voy.,417,tab. 17, fig. 6). 

 Columna 1 teres, Meek and Hayden (1860), Proceed. Acad. Nat. Sci. Philad., VIII, 431. 



Shell small, sinistral, much elongated, 'terete ; volutions twelve to thir- 

 teen, compactly coiled and increasing very gradually in size, a little convex 

 near the upper extremity of the spire, but flattened farther down ; suture 

 linear, and rather faintly marked between the lower whorls, but more 

 distinct above; surface marked by fine obscure lines of growth, which cross 

 the whorls nearly at right angles to the suture. (Aperture unknown.) 



Length, 0.72 inch; breadth, 0.17 inch. 



