226 



DESCEIPTION OF NEW SPECIES OF MOLLUSCA 

 OE THE UPPER EOCENE BEDS AT TABLE 

 CAPE. 



By PEorESsoE Ealph Tate, F.Gr.S., F.L.S.,etc., Coee. Memb. 



[Uead July 7, 1884.] 



POTAMIDES PTEAMIDALE. 



The generic position, assigned to this very striking species, is 

 not unassailable inasmuch as the aperture of the only specimen 

 obtained is broken away ; however, its strong resemblance to 

 P. ebeninium will justify the congeneric reference. As in 

 P. ebeninium^ the last whorl of the fossil is distorted and there 

 is a posterior groove within the aperture. 



Spire acute, apical angle about 30°, of upwards of 10 flat- 

 tened whorls ; body whorl, with the outer lip slightly ascend- 

 ing. Surface ornamented with about 10 flat regularly disposed 

 spiral ribs, crossed by obsolete obtuse sigmoid lines, and on 

 the anterior half with large subacute uodulations, about 12 

 on the penultimate whorl; on the posterior whorls the 

 nodulations are replaced by transverse ridges ; the flat spiral 

 ribs are about as wide as the interspaces, in each of which there 

 is a thread. The last whorl has an asy metrical variciform 

 nodulation above the columella and anterior to the periphery, 

 the space between it and the posterior angle of the aperture is 

 without tubercles as in P. ebeiiinium. The inner lip is much 

 thickened and reflected on the columella. 



Length, less that of the canal, 85 ; hreadth of last whorl, 40 

 millimetres. 



Locality. — Table Cape. E. M. Johnston (one ex.). 



This species differs from the living P. ebeninium in its 

 relatively much greater width, in the nodulations being on the 

 anterior half of the whorl instead of medial, and in its coarser 

 spiral ornament. 



POTAMIDES SEMICOSTATUM. 



Spire acute, apical angle about 15°, of upwards of 12 flattened 

 whorls; body whorl, with outer lip not or only slightly ascending. 

 Surface ornamented with 10 or 12 spiral threads crossed by 

 sigmoid rugae which give rise to a reticulation beneath the 

 posterior suture. The lower half of the anterior whorls with 

 about 10 thick elevated nodulose ridges abrupt on the posterior 

 side ; on the posterior whorls the nodulations are replaced by 

 transverse ridges. In other respects, this species resembles. 

 P. jpyramidale. 



Lengthy 67 ; breadth of last whorl, 22 millimetres. 



Locality, — Table Cape, E. M. Johnston {six exs.). 



