Notes on South African Mollusca. 171 



described from the Rehoboth District, and are known, as yet, from 

 no other locaHty. 



In a large series, the shape of the peristome and the relative 

 position of the umbilicus differ considerably. The peristome may 

 be either acuminate-ovate or nearly circular ; the last whorl, also, 

 may descend very abruptly in front and cause the peristome to be 

 entirely solute, or less abruptly, when the peristome may be almost 

 adnate. The striation is not quite constant, being perceptibly closer 

 in some specimens, both above and beneath, than in others. 



The dimensions vary considerably, a few specimens, taken at 

 random, measuring: — 



Diam. maj. 25-2, min. 20-0; alt. max. 13-5; apert. 12-2x11 mm. 



25-1, „ 20-0; ,. 13-2; „ 12-3x9-8 „ 



22-0, „ 17-0; „ 130; „ 107 x 9-5 „ 



21-8, „ 171; „ 130; „ ll-2x9-5 „ 



This form differs anatomically from the other members of the 

 genus that have been examined in several minor features, one of the 

 most striking being the close convolution of the posterior part of 

 the vas deferens. Although the vas deferens is not wholly detached 

 from the side of the penis, as is said to be the case in the typical 

 form of D. alexandri, it is much more loosely joined to it than in 

 D. coagidmn and D. rogersi ; and it is interesting to note that this 

 gradual separation of the vas deferens from the wall of the penis is 

 correlated with the lengthening and contortion of the latter organ, 

 just as in Trigonephrus lucamis. The jaw is striated, and the caecal 

 prolongation of the penis, described as occurring in the typical form 

 of D. alexandri, is absent from this variety. 



DoRCASiA ALEXANDRI, Gray, var. trivia, 0. Boettger. 



1910 D. alexanderi, Gray, var. trivia, Bttg., Abh. Senckenb. Naturf. 

 Ges. Frankfurt, xxxii. p. 439. PI. XXVIII, f. 3. D.F. 



I have not seen this variety, the following notes on the Type 

 being compiled from information kindly rendered by Dr. Haas. 



Shell intermediate in size between the typical form and var. minor, 

 but of thinner texture. The elevation of the whorls and general 

 form of the aperture and umbilicus are similar to typical alexandri, 

 but the sculpture consists of raised, rather distant costae, from h to 

 1 mm. apart, whereas the fine striae of alexayidri are far closer 

 together, 3 to the mm. on the last whorl. 



