84:6 PROF. G. C. BOURNE ON THE [ISTov. 17, 



yet had the opportunity of studying the anatomy of the European 

 species other th.s.n^flaviattlis. 



I was at first disposed to arrange these three groups as different 

 genera, but have hesitated to do so, because I have perceived 

 that it is impossible to make a reconstruction of the family 

 K'eritidfe on the basis of the slender amount of material at my 

 disj)Osal. I can only indicate the conclusions I have come to and 

 express an opinion upon the probable relationships within the 

 iamily, leaving to future workers in this field the task of testing 

 the validity of my suggestions. 



I am inclined to think, with Moquin-Tandon (28), that the 

 species hitherto classed in the genera Nerita^ Neritina, and 

 Septaria^ agreeing as they do in all fundamental anatomical 

 features, should be grouped together in a single genus Nerita. 

 In this genus I recognize four sections — as a result of further 

 investigations more will probably have to be added, — Nerita, s.s., 

 Paranerita, Septaria, and Xeritina. The section Nerita com- 

 prises (so far as the pi-esent state of our knowledge permits a 

 definite statement) all those truly marine species hitherto classed 

 in the genus Nerita. The section Paranerita includes the tro- 

 pical bra.ckish- and fresh-water forms hitherto classed in the 

 genus Neritina, but which differ from Neritina fluviatilis in the 

 arrangement of the female ducts, in the j)resence of a distinct 

 supra- intestinal nerve, and other minor features. The section 

 Neritina includes Neritina Jiuviatilis and probably all the 

 European, Mediterranean, and Western Asiatic species of 

 Neritina included in the section Theodoxas of Montfort. The 

 subgenus Septaria is equivalent to the genus Septaria of 

 Ferussac. Though I do not regard this as more than a pro- 

 visional arrangement, I shall make use of it, for clearness' sake, in 

 the following part of this paper. It will be found, I believe, 

 that as our knowledge of the iSTeritidfe advances, the various 

 species will fall into a number of geographical groups and sub- 

 groups, each group including marine, estuarine, and fluviatile 

 forms, but the consideration of this suggestion must be left to 

 the latter part of this paper. 



Adopting the provisional nomenclature suggested in the 

 preceding paragraph, the material at my disposal has been as 

 follows : — 



Nerita, s.s. 



N. peloronta Linn. This, the well-known " Bleeding-tooth," is a 

 West Indian species. 



N. plexa Chemnitz. This species is widely distributed in the 

 Indian Ocean. 



N\ lineata Chemnitz. From the Malaysian Islands and X.- 

 Australia. 

 (The above formed pai't of the spirit-collections of the Biitish 

 Museum of Natural History, and I am indebted to Mi'. E, 

 A. Smith for the opportunity of studying their anatomy.) 



