160 Annals of the South African Museum. 



the aperture, but in some much more so than in others, and this 

 expansion influences the shape of the umbilicus, which becomes 

 more crooked and strangulated in proportion to the amount of 

 expansion. This point, together with the more flattened shell 

 and coloured peristome, serves to distinguish ambiguosus at a 

 glance from lucanus, in which none of these characters appear. 

 Fulton mentions the microscopic granular sculpture on the last 

 whorl as being of specific value in his description of ponsonbyi. 

 In the examples which I have seen, this feature, though usually 

 present, does not appear to be quite constant, but, on the other 

 hand, I have never seen a fairly recent specimen in which the 

 peristome did not show traces of colour, and have no reason to 

 doubt that this character affords one of the surest methods of 

 identification. 



I have examined two good series of ambiguosus, from Mossel 

 Bay and Vleesch Bay. The latter shells are more solid, and 

 show more variation than the former. The dimensions of a few 

 specimens, taken at random, are : 



Diam. maj. 33'0 ; min. 26'30 ; alt. max. 19'0 



34-75; 27-0; 19-5 



25-8; 22-2; 15-8 



It is to be hoped that animals of this species may be procured and 

 dissected, in order to find out whether the reproductive system shares 

 those peculiarities which occur in T. lucanus. 



TKIGONEPHRUS AMBIGUOSUS (Fer.)var. COMPACTUS, nov., 1915. 



(PL II, f. 12.) 



Shell subglobose, umbilicate, rather thin, semitransparent, chest- 

 nut-brown above, shading to greyish white beneath ; peristome 

 and callus yellow-brown. Spire moderately elevated, apex blunt. 

 Whorls 5, moderately convex, rather gradually increasing, the apical 

 smooth, remainder covered with close, faint, regular, transverse 

 striae, with occasional faint malleation, especially on the upper 

 surface of the last whorl, and a suggestion of microscopic granular 

 sculpture, which is less apparent than in typical ambiguosus. Suture 

 simple, rather shallow. Aperture rounded-ovate ; peristome 

 narrowly reflexed, ends joined by a thin callus. Columella weak 

 and concave, margin scarcely overhanging the deep, narrow 

 umbilicus. 



