156 J. E. S. MOORE. 



belong to the singular marine fauna for which the lake is 

 famed. 



In the present paper it is my purpose, in the first place, to 

 exhibit the wide morphological difference which exists between 

 these types by a description of the anatomy of Tanganyikia 

 rufofilosa as compared with that of Spekia zonata, both 

 forms having been collected during my expedition to the lake 

 in the summer of 1896. In the second, I wish to show that 

 the morphological characters of both these forms, like those 

 of all the halolimnic species, suggest that they are the con- 

 stituents of a fauna that some ancient sea has left behind. 

 And lastly, I wish to lay emphasis upon the fact that they 

 possess anatomical peculiarities, as a concomitant of their vast 

 antiquity, which are worthy of the closest study. For, quite 

 apart from the fact that these molluscs are zoological curiosi- 

 ties in the sense that they are relics of a departed biological 

 era, it would be difficult to instance any forms possessing a 

 higher scientific value as a means of clearing up the obscure 

 inter-relationship of numerous moUuscan types. 



Tanganyikia rufofilosa. 



The shell of this form is represented in Pi. 14, fig. 1, 

 and was first described by Smith/ from the empty shells 

 obtained by Captain Speke and Mr. Hore. The animals, 

 which I observed alive, have a white, semi-transparent foot, 

 with a very broad, wrinkled, and pigmented snout. The 

 tentacles are not long, and the eyes are situated on tiie posterior 

 base of each. The proboscis is retractile but non-protrusible, 

 like that of Ty phobia. The Littorinoid characters of the 

 operculum are apparent in fig. 1. The buccal mass in this 

 species is extremely small, and the whole radular apparatus is 

 so very little developed, and the radula itself proportionately 

 reduced to such a flimsy structure, that it is by no means easy to 

 find. It actually exists, however, in the bed of a very slight dila- 



» ' Proc. Zool. Soc.,' 1881, p. 288, and 'Ann. and Mag. N. H.,' 1880, vi, p. 426. 



