Notes on South African Mollusca. 143 



constancy of two features, namely, the colour of the peristome and 

 the relative shape of the aperture. 



As regards the former, though exceptions may of course exist, I 

 have never seen T. lucanus or namaqucnsis with any but a white 

 peristome, nor good specimens of the remaining species, globulus, 

 gypsinus, rosaceus, porpliyrostoma and amhiguosns, with other than a 

 deeply coloured one. 



With regard to the second point, we have what may be roughly 

 divided into two forms of aperture, one drooping, the other out- 

 standing. In T. globulus the upper end of the outer lip is com- 

 paratively further away from the columella than in rosaccus, so that 

 it forms with the body whorl an obtuse external angle of about 125°, 

 and imparts to the aperture a drooping appearance. In rosaceus the 

 ends of the aperture appear to be comparatively nearer together, the 

 outer lip consequently leaving the body whorl at a much sharper 

 angle of about 105°, so that the aperture appears to be flatter and 

 more outstanding. 



T. namaqucnsis has the drooping globulus aperture, while 

 T. porphyrostoma and gypsinus have, more nearly, that of 

 T. rosaceus. T. lucanus and ambiguosus form, of course, a 

 separate group. 



Certain species of Trigonephrus exhibit, under a strong lens, 

 irregular patches of granular, or of a kind of close, incised, spiral 

 sculpture. These are usually present where there is least malle- 

 ation, but are of veiy partial and uncertain occurrence, and cannot, 

 in my opinion, be regarded as constant factors in determining 

 the specific position of a shell. 



Trigonephrus globulus (Miiller). 

 (PI. II, f. 1, 2. PI. IV, f. 1, 7, 9, 17, 27. PI. V, f. 1, 9.) 

 1774 Helix globulus, MillL, Verm. ii. p. 68. D. 



Shell large, globose, umbilicate, solid, translucent, early whorls 

 red-lilac above, later violet-blue, with occasional whitish mottling 

 and small dark spots, and a narrow infra-sutural white band ; under- 

 part paler, almost white ; peristome, callus, and interior reddish 

 purple. Spire somewhat produced, apex rounded. Whorls 5, 

 rounded, regularly and rapidly increasing, the apical smooth, 

 remainder covered with very fine, close, transverse striae, with 

 irregular malleation on the upper part of the later whorls and 

 occasional traces of microscopic spiral sculpture. Suture well 

 defined, subcrenulate. Aperture quadrate- ovate ; peristome thick- 



