142 Annals of the. South African Museum. 



endocones. It seems possible, therefore, that in this form the 

 ancestral type of radula has been retained, while in the other 

 members of the family the lateral teeth have become modified to 

 match the central teeth, beginning with those nearest the middle. 

 In most forms the central teeth have lost their secondary cusps, and 

 the ectocones on the lateral teeth have accordingly disappeared ; 

 but in Tri<jo/i<>]>ltnts the central teeth have remained tricuspid, and 

 the lateral teeth may have come to resemble them by the inner 

 portions of their bifid mesocones becoming separated to form small 

 endocones similar to the ectocones. When the teeth in the radula 

 are numerous and arranged in nearly straight transverse rows, it is 

 evident that all those towards the centre will have very similar 

 functions, and that the right and left sides of any one of these teeth 

 will have much the same work to do ; and we might therefore be 

 surprised if the central and lateral teeth did not tend to become 

 like each other, the cusps of the laterals becoming more 

 symmetrical. 



A parallel case occurs among the true Helices of Europe. 

 Nearly all of these have bicuspid lateral teeth, though the mesocones 

 are frequently bifid. But in Helix apcrta, Born, and H. subaperta, 

 Ancey, the laterals are tricuspid, as in Trigonephrus, the inner 

 portions of the mesocones having separated to form true endocones. 



The internal structure of the penis in most of the species reminds 

 one of Wiegmann's figure of the penis of Papidna vitrea.* 



Some of the shells of Trigonephrus have long been a source of 

 trouble to students. 



Miiller's originals of T. ylobulus, rosaceus, and Incanus are pre- 

 served in the Copenhagen Museum. Drs. Nordmann and Jensen 

 of that Museum have kindly compared specimens, furnished by 

 myself, of the shells which usually pass under the above names in 

 British collections with the originals, and have reported that 

 globulus and lucanus, as generally known, are quite correctly 

 identified, and that the rosaceus, though not exactly agreeing with 

 the Type, is undoubtedly conspecific. 



This preliminary matter being determined, it is possible to 

 prescribe means whereby the more puzzling forms may be dis- 

 tinguished. 



The actual shape and size of the shell, and, to a less extent, the 

 coloration and sculpture, may vary greatly in the same species; but, 

 in a large array of material, I have failed, so far, to disprove the 



* Abh. Senckenb. Naturf. Ges., Frankfurt, 1898, xxiv. PI. XXXI, f. 8. 



