464 ME. J. E. S. MOORE OX THE MOLLUSCS [June 18, 



referred respecting the non-occurrence of any of the halolimnic 

 molluscs in Lakes Nyasa and Shirwa, south of Tanganyika. 



With respect, to the actual affinities of the halolimnic molluscs, 

 I did what I could with the material I had brought home after my 

 first expedition, and the results of these investigations have been 

 published in a series of papers in the ' Quarterly Journal of 

 Microscopical Science ' ; but as we had no material for Ihe investi- 

 gation of the type of the genus Paramelania itself, and only one 

 defective specimen of IAmnotrochus ihomsoni, no representatives of 

 Kytra and Stanley a nor of Melania admirabiUs, it is obvious that the 

 investigations of these forms which have already been published 

 were still somewhat incomplete. We have, however, now, as a 

 result of the second Tanganyika expedition, ample material for the 

 complete investigation of every one of the halolimnic types. 



Some portion of the necessary work was accomplished while T 

 was on Tanganyika, with fresh material, and at different times during 

 our journey when time and opportunity arose; and although the 

 observations upon the fuller material now acquired have tended to 

 show that the morphological affinities of those, halolimnic Gastero- 

 poda which I have already described are practically correct, yet at 

 the same time it has become obvious that our conception of the 

 different groups into which the halolimnic Gasteropoda can be split 

 will have to be entirely changed. 



It may be remembered that, in a paper already published ', 

 I found that the anatomical peculiarities of Bythoeeras were 

 those of a fairly primitive cirithoid form, and that there were at 

 t he same time details in the radula of this animal and in certain 

 other portions of its anatomy which proclaimed a very near 

 affinity with the Tympanotomus examined by Bouvier 2 . From 

 the minute similarity in shell-structure which subsists between 

 Bythoeeras and Paramelania damoni, I inferred that the latter had 

 the anatomical characters of Bytlioceras, although I had at the time 

 no anatomical material wherewith to check this conclusion. On 

 the present journey, however, I have obtained abundant materia! 

 for the complete anatomical investigation of both Paramelania 

 damoni and Paramelania crassigranulata, as well as of a new form 

 the conchological characters of which lie halfway between those 

 of Bythoeeras howesi on the one hand and those of Paramelania 

 damoni on the other. All these animals have the peculiar cirithoid 

 organization in general, and the particular features appertaining to 

 their radula? and nerves, which are to be found in Tympanotomus, 

 and which seem to indicate that all these forms have direct 

 phylogenetic relationships with that marine type. 



These forms, then, BytJioceras iridescens, Paramelania damoni, 

 and Paramelania crassigranulata, constitute a group of closely 

 related forms which are distinguished from all the other members 

 of the halolimnic series, and may be described as the Paramelania 

 group. 



1 Moore, J. E. S. : Journ. Micr. Sci. vol. xli. p. 314, and vol. xlii. p. 155. 



2 Bouvier, E. L. : Ann. Sci. Nat. Zool. iii. 1877, pp 125-131. 



