The Non-Marine Mollusca of Portuguese East Africa. 125 



the laterals, and in a few of the outer marginals, a more or less vestigial 

 ectocone is present ; and in some of the latter one or two minute additional 

 cusps can also occasionally be seen on the outer side of the mesocone. The 

 rows of teeth curve slightly forwards on each side. The radular formula is 

 (39+18+1 + 18+40) X 114. 



In the smaller specimen the radula measures 4-5x2 mm., and its formula 

 is (39+15-f 1 + 15+39)X109. The lateral and marginal teeth are similar 

 to those of the larger specimen, but the centrals are abnormal, having two 

 large cusps and three small ones, as shown in text-fig. 4, B. It is not very 

 uncommon to find similar abnormalities among lateral or marginal teeth, 

 but in such cases it is natural to suppose that two adjacent teeth may have 

 become abnormally united. , If, however, the central tooth had become 

 united with the first lateral on one side, we should have expected that this 

 abnormal tooth would have been markedly asymmetrical. As this is not 

 the case, it seems likely that in the present instance we have a mutation in 

 which the central tooth has been almost doubled ; or, if the central tooth 

 be regarded as having been originally formed by the union of two lateral 

 teeth, perhaps we may be dealing with an example of reversion in which 

 this union has been abnormally arrested before becoming complete. That 

 this abnormal tooth is weaker than the others is suggested by the fact that 

 it is missing from several of the rows at the front end of the radula. 



The buccal mass is large and muscular, and the radula-sac is completely 

 embedded within it, instead of its hind end projecting as a papilla. The 

 oesophagus leads into a capacious crop (fig. 7). The salivary glands lie 

 on each side of the crop, but are loosely united above it ; they are very 

 large, especially the left one. The nerve-ring surrounds the oesophagus, 

 salivary glands, and buccal retractors, behind the buccal mass. The various 

 ganglia are enclosed in much connective tissue, and are rather closely 

 approximated, the commissures and connectives being short. 



Free retractor muscles (fig. 7). — The buccal retractor and the two 

 tentacular retractors are separate almost from their origin. The buccal 

 retractor divides into a right and a left portion, separately innervated, a 

 considerable distance behind the buccal mass. The retractor of the right 

 upper tentacle passes between the penis and the vagina. Another muscle, 

 quite distinct from the last, runs along the right side of the animal to the 

 head. No definite muscle could be found passing from the columella to 

 the foot. The penial retractor arises from the diaphragm. 



Reproductive organs (fig. 7). — Unfortunately the reproductive system 

 was not fully developed in either of the specimens examined, but it is 

 evidently of a comparatively simple type. The receptaculum seminis is 

 large and bluntly pointed posteriorly, and is borne on a rather short recep- 

 tacular duct. The vagina is of no great length, and seems to be without 



