146 Transactions of the Royal Society of South Africa. 



radular formulae of the two specimens examined: (5+5+l-{-5-|-6)X 82, 

 (6+5+1+5+5) X 80. 



The radula of this species differs from that of Trachycystis rudicostata 

 in the teeth being shorter and relatively broader, and in there being fewer 

 of them in each transverse row. These differences, however, are not very 



^^^^Y^^^^T^^^ 



B 



Text-fig. 12. — Trachycystis soror Conn., Vengo Mountain. 



A. Roof of mantle-cavity seen from the outside, showing kidney, etc. (slightly diagram- 



matic) ; x28. 



B. Half of a transverse row of teeth from the radula ; X 1400. 



great, and it is probable that the two species are fairly closely related, not- 

 withstanding the dissimilarity in the apical sculpture of their shells. 



Trachycystis pura Conn., 1922. 

 (Plate IV, fig. 15.) 



1922. Trachycystis pura Conn., A.M.N.H. x, p. 118. D. 



Hah. L. Marques. Mount Vengo, 5500 ft. (type, Cressy). 



Cape Province. Thomas River, Cathcart (Miss Davidson). 



Easily distinguishable from its minute confreres by its milky shell and 

 comparatively strong, close, radial striae. 



The kidney (text-fig. 13, A) extends from the pericardium upwards to 

 the rectum, and has two anterior prolongations : a lower one, which is 

 about I mm. long, occupying the usual position between the heart and 

 pulmonary vein, and the primary ureter, which arises from its front end ; 

 and an upper prolongation, which is nearly as large as the lower one, and is 

 situated between the rectum and the posterior end of the secondary ureter. 

 The kidney contains numerous spherical or oval concretions, which are 

 largest in the upper anterior prolongation, where some of them attain a 

 diameter of -02 mm. 



The jaw is about -105 mm. long, slightly curved, and very thin, but shows 

 traces of vertical folds. 



