164 Annals of the South African Museum. 



The height of spire varies greatly. Von Martens gave the 

 measurements of his larger shell as: Diam. maj. 24, min. 19; alt. 

 20 mm. ; and his smaller one, as measured by myself, is : Diam. 

 maj. 20, min. 15'4 ; alt. max. 14 mm. Most of the examples 

 brought by Rogers from Little Namaland are comparatively lower 

 in the spire, measuring 25'3 x 20'5 x 15'5 ; 22-8 x 19 x 15-6 ; 

 22-6 x 18-5 x 15-2; 22-5 x 18-2 x 13-8; and 21-5 >: 17-3 x 13-6 mm. 

 In all of these the umbilicus is a little smaller and less overhung by 

 the columellar margin than in the Type pair, but the discrepancy 

 is not sufficient to necessitate varietal distinction. The callus is 

 variable, being entirely absent in some fully formed shells and 

 quite distinct in others. 



This species might perhaps be regarded as one of the more primi- 

 tive members of the genus, though the radula is of a somewhat 

 specialized type. In the form of the shell and reproductive organs 

 D. coagulum approaches Trigonephrus more nearly than do the other 

 known species of Dorcasia ; nevertheless the sculpture of the shell, 

 the tripartite footsole, the form of the kidney, the internal structure 

 of the penis, and especially the unicuspid central and lateral teeth 

 of the radula, prove beyond doubt that this species belongs to the 

 genus Dorcasia. 



The shell is peculiar for South Africa, being far more reminiscent 

 of the Mediterranean H. vermiculata, Miill., than of the neighbouring 

 forms of its own genus. 



DORCASIA ROGERSI, sp. nov., 1915. 

 (PI. Ill, f. 2, 3. PL IV, f. 15, 23. PL V, f. 7. Text-fig. 1, C, D.) 



Shell rather small, umbilicate, depressed orbicular, fairly solid, 

 translucent, calcareous, creamy white, with slight, irregular, fawn 

 blotches and spots, which are chiefly present on the third whorl ; 

 apex pale corneous ; peristome white. Spire depressed, but each 

 whorl, in profile, projects clearly above the next ; apex rounded. 

 Whorls 5, narrowly rounded, regularly increasing, the two apical 

 smooth, remainder prettily sculptured with close, transverse striae, 

 which become rather coarser and less regular towards the aperture 

 and are hardly visible on the base. Suture deep, very little 

 crenulate. Aperture almost circular ; peristome reflexed, ends 

 joined by a very slight callus. Columella very weak, margin slightly 

 thickened and reflexed, but not approaching the umbilicus, which is 

 perspective and very deep, but not wide. 



Diam. maj. 21-1, min. 17-5; alt. max. 11-7 ; apert. 9-7 X 8'9 mm.; 

 ends of peristome 4'3 mm. apart. 





