464 MR. J. E. s. MOOEE ON THE MOLLUSCS [June 18, 



referred respecting the non-occurrence of any of the halolimnic 

 niollnscs in Lakes Nyasa and kSbirwa, south of Tanganyika. 



With respect to the actual affinities of the halolimnic molluscs, 

 I did what I could with the material T 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 the investi- 

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

 defective specimen of Limnotrochvs tltomsoni, no representatives of 

 Kytra and Stanleya nor of Melania admirabilis, it is obvious that the 

 in\'estigations 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 I 

 was on Tanganyika, vi'ith fresh material, and at different times during 

 our journey when time and opportunity arose ; and although the 

 observations upon the fxiller material now acquired have tended to 

 show that the morphological affinities of those halolimnic Grastero- 

 pods 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 Gasteropods 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 Bijthceeras were 

 those of a fairly primitiA'e cirithoid form, and that there were at 

 the 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 Tymjyanotoymis examined by Bouvier^. Froia 

 the minute similarity in shell-structure which subsists between 

 Bythoceras and Paramelania damani, I inferred that the latter had 

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

 no anatomical material wherewith to check this conclusion. On 

 the present journey, however, I have obtauied abundant material 

 for the complete anatomical investigation of both Paramelania 

 damoni and Paramelania crassif/ranulata, as well as of a new form 

 the conchological characters of which lie halfway between those 

 of Bythoceras 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 radulse and nerves, which are to be found in 'J'ympanotomus, 

 and which seem to indicate that all these forms have direct 

 phylogenetic relationships with that marine type. 



These forms, then, Bythoceras 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. : Joum. Micr. Sci. vol. xli. p. 314, and vol. xlii. p. 155. 



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



