SMITH : MOLLUSCA OF LAKE TANGANYIKA. 81 



of the shell is quite different. I may here mention that the figure 

 given by Mr. Moore of ISpehia is nothing like that shell, and I can 

 hardly believe that it was taken from it. Neridomus, or Neritodomus 

 as emended by Fischer, is a globose shell with a convex columellar 

 callus, such as may be observed in some species of Naticidse and 

 Neritina, whei'eas the most remarkable basal excavation in Spekia at 

 once distinguishes that species. In this respect and in general form 

 it bears a strong resemblance to Lacunopsis Jullieni, Deshayes, and 

 L. Harmandi of Poirier, fresh-water forms from Cambodia, but probably 

 the animals are very different; at all events, they do not agree in 

 respect either of the radula or opercula. 



7. Melania admtrabilis and Cekithium subscalaeiforme. 



In respect of these fonus Mr. Moore writes : — " There is among the 

 Gastropods of the halolimnic group a very remarkable and characteristic 

 shell which Smith named Melania admirabilis. It is a Cerithoid form 

 totally unlike any other living type which is known, but it has been 

 found by comparison that it is practically indistinguishable from the 

 Inferior Oolitic fossil known as Cerithium suhscalariforme.^' I certainly 

 cannot agree in the above opinion, and I have no hesitation in saying 

 that, in this instance, the supposed resemblance is purely imaginary. 

 The Melania admirabilis possesses all the characters of that genus, 

 and is not unlike in style of sculpture certain other species, for 

 example, Melania cancellata^ Benson, M. Henriettm, Gray, M. Gredleri, 

 Bttgr., and others. Longitudinal costae upon the whorls with spirals 

 around the base of the body- whorl are features which occur in a con- 

 siderable number of species. The aperture is exactly that of Melania, 

 and bears no resemblance to that of Cerithium, which has a distinct 

 anterior or basal canal, entirely wanting in true Melanias. All the 

 specimens hitherto found of this species have been dead shells and 

 devoid of epidermis. In this condition they have a less fluviatile 

 appearance, and, being solid, they might at a first glance be mistaken 

 for a marine form. However, the exact agreement with Melania, in 

 every respect, leaves no doubt as to their true location. In regard to 

 solidity and marine aspect I would again call attention to Melania 

 brevis, D'Orbigny, from the rivers of Cuba, also to many species of 

 fresh-water Neritina, the Lithoglyphi of the Danube, Pachydrobia, 

 Lacunopsis, and Jullienia from Cambodia, Melanopsis from Syria, and 

 the remarkable genus Miratesta from Celebes. All of these have quite 

 as thalassoid an appearance as many of the Tanganyikan species. 



8. TiPHOBiA and Purpukoidea. 



This is the final comparison which Mr. Moore suggests with regard 

 to these Tanganyikan shells, and, I must confess, it is a very un- 

 fortunate one. ile observes, " Tiphobia of Tanganyika is matched by 

 an Oolitic fossil genus, Purpuroidea, from which it is very difficult, 

 if not impossible, on conchological grounds, to distinguish it." As 

 a conchologist of some experience, I fail to perceive the great resem- 

 blance between these forms, and we might just as well compare 



