200LOQY. 459 



from Tanganyika, having very much the appearance of a marine form." 

 What particular "marine form," if any, is meant is not specified, but 

 the figure reminds one of a Flanaxis. 



Two other sub-genera or genera complete the list of peculiar types 

 discovered in the African lake. They are — 

 Pakamelania (E, a. Smith, P. Z. S. L., 1881, p. 558) 

 Keothauma (E. a. Smith, P. Z. S. L., 1880, p. 349 ; 1881, p. 293). 



The former is a Melanoid; the latter a Viviparine gastropod with the 

 labrum "deeply emarginate" and reflected. 



The discovery in a single body of water of such aa association of 

 peculiar and limited types, and with such a facies is unexampled in the 

 annals of conchologj'. In the opinion of Mr. Smith, three of these, es- 

 pecially the species of lAmnotrochus and Syrnolopsis, "have all the 

 appearance of being modified marine types; and such is probably the 

 case," he adds, for, "judging from the geology of the neighborhood, 

 Tanganyika at some remote epoch has been an inland sea, the saltness 

 of whose waters has almost entirely vanished, leaving only a peculiar 

 taste, which can scarcely be described as brackish" (P. Z, S., 1881, 276- 

 277). Their presence involves one of the most difficult malacological 

 problems, thinks Mr. Crosse (Journ. Conchol. (3), t. 21, p. 303); but 

 while he retains lAmnotrochus in the Littorindce^ he is very doubtful 

 whether the soft parts of Syrnolopsis will confirm its reference to the 

 same family with Syv/iiola. 



It is very regrettable that the soft parts of the several genera discov- 

 ered should remain unknown. The opercula seemed to have been intact 

 in some of the shells, and probably, therefore, the lingual ribbons could 

 with proper care have been found. Their examination alone would have 

 permitted a determination, at least, approximative, of the mollusks, 

 aflQnities. Until such examination the question of relationship must 

 remain doubtful. It may be suggested, however, that the variations of 

 the shells, considerable and remarkable as they are, are not incompati- 

 ble with their association with the Melaniids, for they can be derived 

 from the same type. But whether the new genera are much modified 

 Melanians, (or Viviparids,) or related to marine forms, or representatives 

 of even peculiar families, must remain unsettled till the lamentable 

 neglect to search for and examine the odontophores at least is repaired. 

 Meanwhile the most conservative course would be to associate them with 

 doubt in the family of Melanians. The deductions of Mr. Smith as to 

 the geological relations of the lake forms do not appear to be warranted. 



Lake Tanganyika has now contributed to conchology 32 species, rep- 

 resenting 19 genera; 20 species and G genera or sub-genera have not 

 been detected elsewhere; 8 species are known to bo also found in the 

 Nile. 



As to the Faramelmiice, Dr. C. A. White, of Washington, has ex- 

 pressed the opinion that there is a generic identity between those species 

 and the Fyrgulifera humerosa of Meek, described about five years 



