Notes on South African Mollusca. 167 



abruptly. Aperture almost circular, the ends joined by so thick a 

 callus as to make the peristome practically continuous. Umbilicus 

 wide and deep, as in the Type, and it is owing to this feature, in 

 particular, that I agree with von Martens in considering the two 

 shells conspecific. 



The measurements of this smaller form are : Diam. maj. 19"3, 

 min. 15"6 ; alt. 9-4 mm. 



The abrupt final descent of the last whorl, which causes the entire 

 peristome to lie flat on the ground and conceal the aperture when 

 the shell is in its normal position, is not of such specific value as 

 it was considered by von Martens. In large series, both of D. alex- 

 anclri and its var. rotimdata, I have seen some examples in which 

 this feature is very marked, while, in the generality of specimens, the 

 descent is either less abrupt or less extensive, so that the interior of 

 the empty shell is plainly visible from the front, when the shell is 

 laid in its normal position. 



As will be seen from the figures, the Type, with its extraordinarily 

 flattened spire and small aperture, looks almost like an abnormal 

 example ; but Dr. Thiele informs me that there are two more 

 subfossil shells, from Kuibis, in the Berlin Museum, both very 

 similar to the Type, so that the form is probably well established 

 and distributed, and should be easily distinguishable from others of 

 the genus. 



DoKCASiA ALEXANDKi, Gray. 



(PI. Ill, f. 5.) 



1838 Dorcasia alexandri, Gray, Alexander's Expedition, ii. 

 p. 268. D. 



Shell large, depressed-globose, rimate-perforate, rather thin, 

 translucent, type bleached white, but normally corneous ; peri- 

 stome white. Spire but little raised ; apex obtuse. Whorls 5, the 

 later rapidly increasing, all but the 1^ apical covered with very fine 

 and close, regular, curved transverse striae, almost disappearing on 

 the base ; last whorl swollen, so that it is nearly as high as the 

 spire, ascending slightly at the suture and descending very 

 abruptly, nearly perpendicularly, in front, almost concealing the 

 aperture. Suture well defined, simple. Aperture rounded ovate ; 

 peristome continuous, free, margins not thickened but widely and 

 strongly reflexed, though not overhanging the perforation, which is 

 narrow, strangulate, and so eccentric that a portion of the penultimate 

 whorl is fully disclosed. 



