The Non-Marine Mollusca of Portuguese East Africa. 181 



teeth, however, are relatively not quite so small as in the adult. The cusps 

 of the other teeth are slightly narrower than they are in the full-grown 

 radula, and the endocones are a little more distinct. 



The radula of this species differs from those of Subulina octona (Brug.) 

 and allied forms chiefly in the very inconspicuous endocones of the lateral 

 teeth. Since, however, the ndocones are more prominent in the marginal 

 teeth, and are rather better developed in the embryo than in the adult, it 

 seerns likely that this species has been evolved from a form having the 

 more obviously tricuspid lateral teeth found in most of the Stenogyrinae. 

 The particularly degenerate central teeth also suggest that in its radula 

 this species is less primitive than many of its allies. 



28 



Text-fig. 21. — Subulina chiradzuluensis (Smith), Macequece. 



A. Representative teeth from the radula of an embryo from the uterus ; X 600. 



B. Representative teeth from the radula of a mature specimen ; X 600. 



The course of the alimentary canal will be seen from PL V, fig. 14. 

 The crop is unusually narrow, but perhaps this may be due to the relatively 

 large embryos swelling the genital ducts to such an extent as to leave little 

 room for the other organs in this region. The salivary glands are long, and 

 are situated a little further forward than usual. They are united with 

 each other above the alimentary canal. 



Free retractor muscles (PL V, fig. 15). — The columellar muscle divides not 

 far from its origin into a right and left division. A little further forward 

 the right division gives off a broad " tail retractor " to the foot. The 

 remaining portion of the muscle runs forward as the right tentacular 

 retractor, but just before it divides into the retractors of the upper and 

 lower tentacles, it gives rise to the penial retractor, which, as in most 

 members of this family, does not arise from the diaphragm. The muscles 

 going to the lower tentacle and the front of the head pass to the left of the 

 penis, but the retractor of the right upper tentacle passes between the penis 

 and the vagina. 



The left division of the columellar muscle divides rather far forward 



