THE MOLLUSCS OF THE GEEAT AFRICAN LAKES. 155 



The Molluscs of the Great African Lakes. 

 III. Tanganyikia rufofilosa, and the Genus Spekia. 



By 

 J. E. S. Moore. 



Witli Plates 14—19. 



On the coast line formed by the red sandstone and con- 

 glomerate precipices which flank tiie picturesque shores of 

 Lake Tanganyika there are to be found a number of rock 

 molluscs, which dwell upon the submerged stones, much 

 in the same manner as the periwinkles do upon the half-tide 

 rock faces of the ocean coasts. Of these small Gastropods, 

 what have appeared to be at least three distinct species have 

 been known, but hitherto only by the characters of their empty 

 shells, and in tlie absence of all other information they have 

 been regarded by tiie conchologists as approaching the genus 

 Lithoglyphus.^ In the literature, one of these forms, L. 

 neritinoides, still bears that generic name, but the species 

 rufofilosa was eventually placed by Cross in what he supposed 

 to be an allied but separate genus, under the name of Tangan- 

 yikia, while the original L. zonatus was placed by Bourgui- 

 gnat in the genus Spekia. 



No shells exactly similar to these have been found, hitherto, 

 outside the confines of the great lake in which they were 

 originally observed by Speke ; and from this very renjarkable 

 fact we might suspect, without further investigation, that they 



' That is as members of the family Hydrobiidje. 



