TtlE MOLLUSCS OP THK GKEAT AFRIdAN LAKES. 157 



tation of the gullet (PI. 14, fig. 3, rat/.), and this dilatation must 

 be taken as the only indication of the almost entirely undeveloped 

 buccal mass. The radular dentition is interesting and some- 

 what peculiar; a single row of the delicate teeth is represented 

 in fig. 5. In many ways the dentition suggests physiological 

 adaptation. Both the rows of lateral teeth are very much alike, 

 and there does not appear to be any difference in the relative 

 size of the serrations on the head of either the outer or the 

 inner of these teetli. In this feature the lateral teeth 

 resemble those of Modulus lenticularis, as figured by 

 Troschel, and to a certain extent the whole row of teeth 

 approximates to this type ; but on closer examination the 

 admedian, no less than the median tooth itself, differs widely 

 from any of the more normal melanioid forms. The predominant 

 denticle on the reflexure of the admedian teeth, which is such 

 a constant feature of so many radulas (see the radula of 

 Spekia zonata (PI. 18, fig.3, joreflf.),is here quite wanting, but 

 it is clearly visible in TroscheFs figure of Modulus to which 

 I have referred. Neither is there any posterior denticle on the 

 median tooth of T. rufofilosa which would either correspond 

 to that of Modulus, or that on the median teeth of the forms 

 truly belonging to the genus Lithoglyphus. The admedians, 

 laterals, and to some extent the medians of this radula 

 approximate to those of Tympanotomus fuscatus given by 

 Troschel, and in a more general way to those of Plan ax is 

 sulcatus (Lam.); and from these characters of the radula we 

 might conclude with certainty that the genus Spekia has little 

 or no connection with the Hydrobiidae, to which family it 

 has been hitherto thought to belong. 



In all the specimens of T. rufofilosa which I examined, the 

 mouth, oesophagus, stomach, and rectum were crammed with 

 sharp rock fragments, about the size of a pin's head ; and it is 

 a curious fact that these animals should thus exhibit a pro- 

 pensity to fill themselves with stones, while at the same time 

 the radula, or normal rasping apparatus, is almost entirely 

 lost. The salivary glands are simple and somewhat long. 



The oesophagus is narrow, and opens posteriorly in the 



