MOORE: ON- THE FAMILY MELANIID^^i;. 231 



type of nervous sytem. The cerebro- and pedo-pleiiral connectives 

 are not long, and the pedal ganglia possess no scalariform pedal cords. 



This type of nervous system is encountered in the Cerithiidge, and 

 in a slightly modified form among the Turritellidse, the Typhobiidse, 

 the Strombidae, the Aporrhaiidse, and the Xenophoridse. 



In the genus Melanopsis, on the other hand, Bouvier found that the 

 nervous system is widely diiferent, being much more comparable to 

 that met with in the genera Fivtpara, Cyclopho7^iis, and their allies. 

 Thus, among the different animals which have hitherto been considered 

 as sufficiently closely related to form the members of a single family, 

 we find types of organization that are singularly diverse. For purely 

 conchological reasons three genera of moUusca occurring in Lake 

 Tanganyika, namely, Nassopsis, Paramelania, and Typhobia, have 

 also, until lately, been regarded as belonging to the Melaniidse ; and 

 since I have had an opportunity of fully examining the anatomical 

 characters of these forms, it will be of interest to review in the light 

 of Bouvier's work the conclusions to which my researches have led. 



In a recent paper ^ I have described the anatomy of Typliolia in 

 detail, with that of the allied Tanganyikan genus Bathanalia, and have 

 therein made it evident that both these syphonate gastropods differ 

 almost as widely from Melania amarula in one direction as Melanopsis 

 does in another. In Typhohia and Bathanalia the nervous system is 

 on the same general plan as in Melania amarula, or in Aporrhais ; but 

 in its general anatomy, as for example in its radula, Typhohia corre- 

 sponds much more closely to the latter than to the former of these two 

 genera. I was thus led to dissociate Typhobia and Bathanalia altogether 

 from the Melaniidse, and place them in a new family, the Typhobiidae, 

 which, in its general anatomical characters, finds its nearest relations 

 in Strombus and the Aporrhais group. 



Nassopsis, a full account of the anatomy of which will, I hope, 

 shortly appear in the Quart. Journ. Micros. Sci., exhibits yet another 

 type of nervous system, the cerebral ganglia being widely separated 

 from each other. The pleural ganglia are separated from, and are 

 distinctly below, the cerebral ganglia, as in Vivipara ; but the right 

 pallial nerve, instead of originating in two roots, as in the latter 

 genus, here springs as a single trunk from the sub -intestinal ganglion, 

 which is put into direct connection with the pleural ganglion by 

 a stout cord. Thus Nassopsis is, according to Bouvier's definition, 

 strongly zygoneurous on the right side. 



These peculiarities, however, are not the only differences between 

 this and the preceding types. We find that in Nassopsis the cerebral 

 ganglia are secondarily united by a very distinct labial commissure, 

 just as in the Rhipidoglossa and such Archi-taenioglossa as Ampullaria 

 and Vivipara, and to make the homology between the nervous system 

 of Nassopsis and the more primitive Archi-taenioglossa complete, we 

 find further that the pedal ganglia are continued backward into long 



1 Quart. Journ. Micros. Sci., vol. xli (1898), p. 181, 



