The Non-Marine Mollusca of Portuguese East Africa. 147 



The radula of tlie specimen examined (text-fig. 13 B) measures -32 X -105 

 mm when flattened out, but the snail may not have been quite full-grown. 

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

 Their mesocones are large, those of the lateral teeth extending a little 

 beyond the posterior edges of the basal plates. Their ectocones and 

 endocones are short, but the endocones of the lateral teeth are shghtly 

 larger than the ectocones-an unusual feature. The first latera teeth on 

 each side are disproportionately large, being much bigger than the centra 

 teeth • probably this is connected with the fact that the number of lateral 

 teeth is unusually small. In the marginal teeth the basal plates are much 

 shorter, especially in the outer teeth, which are remarkably short m pro- 



,^^^V^^^^^ 



f^^^^ 



B 



Text-fig. U.—Trachycyslis jnira Conn., Vengo Mountain. 



A. Kidney, heart, etc., seen from the outside (slightly diagrammatic) ; x36. 



B. HaK of a transverse row of teeth from the radula ; X 14UU. 



portion to their breadth. The endocones of the marginal teeth have longer 

 cutting points, but they are often split into two cusps. The ectocones o 

 the marginal teeth also become divided into two, or sometimes three, small 

 cusps, but thev are very much shorter than the endocones and mesocones. 

 The transverse" rows of teeth are not straight, but slope backwards from the 

 centre in the region of the lateral teeth, and forwards again m the region ot 

 the marginal teeth. The radular formula is : (6+3+1 + 3+6) X 66. 



It will be seen that in this species the radula, as well as the shell and 

 kidney, is of a slightly specialised type, although it agrees with the other 

 members of the Endodontinae in all its more important characters, ihe 

 backward trend of the lateral teeth, and the large size of the first one on 

 each side, make this radula easy to distinguish from any of the others 

 illustrated in this paper. In some respects it resembles the radula of the 

 American species Helicodiscus lineatus (Say),* although that species has a 

 much smaller and narrower central tooth. 



* See Watson : Proc. Malac. Soc, vol. xiv, 1920, p. 12, fig. 4e. 



