Notes on South African Mollusca. 137 



neither with the right parietal ganglion, as in the Zonitidae, nor 

 with the left, as in the Hclicidae. Left parietal ganglion nmch 

 smaller than the other two visceral ganglia. 



Digestive system. Jaw of the usual crescentic form, with a 

 slight median projection on the lower edge (except in Trigonephrus 

 globulus) ; always without ribs, but covered with fine vertical striae 

 (see PI. IV., figs. 17-24). In Trigonephrus even fainter, though 

 broader, oblique striae can also often be distinguished near the lower 

 edge, diverging from the central projection. 



Eadula varying in size from 3'9 X l - 3 mm. in Dorcasia roycrsi to 

 7f x4J mm. in Trigonephrus rosaceus, and possessing from 8,300 

 to more than 15,000 teeth (the number of teeth in each transverse 

 row being a little less than the number of rows). Transverse rows 

 straight or trending very slightly forward on each side. Bases of 

 teeth quadrate, usually with a short flange projecting in front. 

 Marginal teeth generally bicuspid ; lateral and central teeth tri- 

 cuspid in Trii/oiicpJirus, unicuspid in Dorcasia; but the transition 

 from marginal to lateral teeth is very gradual. Central teeth not 

 very much smaller than the laterals. (See text-fig. 2, B, and 

 PI. IV., figs. 9-16).* 



Buccal mass muscular and rather large, the odontophoral 

 muscles reaching back on each side as far as the end of the radula- 

 sac in adult specimens of Triijoiiephrus porplujrostoma and T. 

 namaquensis, so that in these species the end of the sac no longer 

 projects as a papilla (compare PI. IV., figs. 7, 8). Oesophagus 

 and salivary ducts short (see PI. IV., figs. 25, 26). Salivary glands 

 generally meeting both above and below the alimentary canal, but 

 only loosely united with each other. Crop narrow in the majority of 

 specimens, but sometimes much distended, as in the example 

 figured by Pilsbry.f In Dorcasia coagulum and D. royersi the con- 

 nective tissue surrounding ths crop and salivary glands is darkly 

 pigmented. Stomach sac-shaped, consisting of an anterior thin- 

 walled portion in continuation with the crop, and a posterior portion 

 with thicker muscular walls, from which the intestine passes 



* The radula in this sub-family seems especially liable to malformation. In a 

 specimen of Tritjoncphrus globulus belonging to Professor Gwatkin, as well as in 

 one of the examples of Dorcasia alexandri var. rotundata dissected by the writer, 

 the teeth in ten or fifteen adjacent transverse rows were all greatly shortened, and 

 some of the outer marginals were suppressed altogether. In another specimen of 

 T. (jlobidiis five of the teeth in each transverse row were abnormally large, being 

 formed, in at least some cases, by the union of two adjacent teeth ; and there were 

 thus five separate longitudinal rows of abnormal teeth in the radula. 



f Proc. Mai. Soc., 1905, vi. PI XIII, fig. 8. 



