148 Transactions of the Royal Society of South Africa. 



Trachycystis vengoensis Conn., 1922. 

 (Plate IV, fig. 16.) 



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



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



The jaw measures about -Ix -02 mm. It is curved, very thin, and has 

 little or no visible sculpture. 



The radula (text-fig. 14) measures •29X-11 mm. when flattened out. 

 The central and lateral teeth are tricuspid, with quadrate basal plates. 

 Their mesocones are rather long, reaching the posterior edges of the basal 

 plates, the cutting points being short in the inner teeth but longer in the 

 transitional teeth. Their ectocones are rather small ; their endocones 

 are also small and a little narrower than the ectocones in the inner lateral 

 teeth, but become longer in the transitional teeth, with larger cutting 



Text-fig. 14. — Trachycystis vengoeiisis Conn., Vengo Mountain. 

 Half of a transverse row of teeth from the radula ; X 1600. 



points. The marginal teeth have much shorter bases ; their mesocones 

 have rather long points ; their ectocones are divided into two or three 

 minute pointed cusps, and their endocones, which are slightly longer 

 than the ectocones, also tend to split into two. In the radula figured 

 the third marginal tooth on the right side is abnormally without an 

 endocone. The transverse rows of teeth are almost straight in the middle, 

 but bend slightly forwards on each side in the region of the marginal 

 teeth. The radular formulae of the two specimens examined are : 

 (6+6+l + 6+6)x72, and (6+6+l + 6+6)x80. The radula is thus of 

 the normal type found in the Endodontinae, although the teeth are 

 very small. 



The nearest relations to this microscopic species have been described 

 under the names of Pyramidula {Gonyodiscus) iigandana Smith,* and 

 Gonyodiscus smithi Dautzenberg and Germain, f the shells of both of which 

 so closely resemble that of vengoensis that they must surely be congeneric. 

 It differs from the type of ugandana, which is a larger shell, in having an 

 infinitesimally sharper and narrower suture, finer sculpture, a narrower 



* Joum. of Conch, x (1903), p. 317. 

 t Rev. Zool. Africaine iv (1914), p. 19. 



