THE MOLLUSCS OF THE GREAT AFRICAN LAKES. 183 



consequently enabled to dredge in water that varied from 

 500 to 850 feet in depth. Eventually in this manner, during 

 the months of June and July, about a hundred Typhobias were 

 obtained alive. Of these some were examined on the spot, some 

 preserved in various ways, stored in spirit, and eventually brought 

 back. The living Typhobias were associated with another 

 deep-water Gastropod, also alive, a brief description of which 

 will be found at the end of the descriptive part of this paper. 



Except in the characters of the shell, this new genus is 

 almost identical anatomically with T. Horei, consequently it 

 is unnecessary that I should do more than point out in what 

 it differs from the form already known. 



External Characters.— The general appearance of a 

 living Typhobia is seen in fig. 1. They are always very active 

 when brought up from the deep water they inhabit, probably 

 being uncomfortable through the decreasing pressure. The 

 tentacles are very long and slender, and the eyes completely at 

 their base ; the snout is wrinkled and very much pigmented 

 on the upper surface, and it is so long and slender as to suggest 

 the ordinary protrusible snout or introvert of Prosobranchs ; 

 on dissection, however, it is seen to be simply elongated ex- 

 ternally, very retractile, but, like that of Pterocera, not intro- 

 vertible in any sense. The foot is very broad, and of the same 

 pale semi-transparent yellow as that of Anodonta. The mantle 

 is prolonged into the well-marked anterior and posterior 



siphons (fig. 2). 



As is the case with many other fresh- water Gastropods, the 

 shells of Typhobia Horei vary to a remarkable degree; 

 indeed, the extreme forms when isolated, and not linked to- 

 gether by the innumerable intermediate forms which actually 

 occur in Tanganyika, differ so widely that the French concho- 

 lo»ist^ Bourguignat regarded these differences as sufficient to 

 split the genus up into four species, under the new name 

 of Hylacantha ; his four so-called species being respectively 

 H. Horei, H. Bourguignati, H. longirostris, and H. 

 Jubertii. Had this author, however, been able to obtain 

 1 ' Ann. des Sci. Nat./ septieme serie, ix, x, 1390, p. 125. 



