876 W. H. HUDLESTON, ESQ., M.A., F.R.S., ON THE ORIGIN 



APPENDIX TO PAPtT I. 



Notes on the comparisons between the Halolimnic Gasteropods 



AND certain fossils FROM THE INFERIOR OOLITE— TOGETHER WITH 

 AN ABSTRACT OF Mr. MoORE's STATEMENTS REGARDING THE 

 MOLLUSCA OF TANGANYIKA GENERALLY. 



* Forty-six species of mollusca are enumerated {The Tanganyika 

 Problem, p. 138), consisting entirely of Gasteropods and Lamellibranchs, 

 the former preponderating. Of the latter are a number of distinct 

 specific forms supposed to be related to Unio. Many of the Gasteropods 

 belong to normal genera, such as Limncea (four species), Isidora (two), 

 Phyopsis (one), Planorbis (three), Ampullaria (two), Vivipara (one), 

 Cleopatra (one), Melania (three). There is also the very fine Vivipam- 

 like genus, Neotliauma, Smith, which cannot in any sense be regarded as 

 halolimnic. Mr. Moore further observes that the normal fresh-water 

 molluscs found in Tanganyika are specifically distinct from the represen- 

 tatives of the same genera occurring in the neighbouring lakes. Exclud- 

 ing Neothauma there are fourteen Gasteropodean types (p. 218) judged by 

 their conch ological characters, generically distinct, as follows, viz. : — 



Typhohia. Spekia. 



Bathanalia. Nassopsis. 



Limnotrocus. Syrnolopsis. 



Chytra. Stanleya. 



Parameiania. Reymondia. 



Bythoceras. Horea. 



Tanganyicia.. Ponsonhya. 



Out of these the following are regarded as specially representing the 

 halolimnic molluscs, and are classified in six groups, viz. : — 



Typhohia and Bathanalia, Tanganyicia, Limnotrochus and Chytra^ 

 Spekia, Parameiania and Bythoceras, Nassopsis. 



It is more especially the above forms which are regarded as 

 homseomorphic with certain fossils, chiefly of the Inferior Oolite, and 

 this resemblance has impressed Mr. Moore so strongly, that he is 

 disposed to consider these groujDs as the partially modified descendants 

 of the old Jurassic molluscs. 



As most of these comparisons were made with fossils in my own 

 collection, I have endeavoured, in those cases where it has been possible 

 to procure the particular Tanganyika shells, to check the resulting 

 determinations, of course on conchological lines solely. 



1. Melania admirahilis, Smith, loith Cerithium suhscalariforme, UOrbigny. 



N.B. — These shells are not referred to in the above list. On pp. 219 



and 353 of the Tanganyika Problem are back and front views of the 



* It is probable that this is not an absolutely full list. 



