92 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



DESCEIPTIONS OF THE GENERA BATHANALIA AND BYTHOCERAS, 

 FROM LAKE TANGANYIKA. 



By J. E. S. MooRE, 

 Zoological Laboratory, Royal College of Science, London. 



Read \Zth May, 1898. 

 Among the molluscs which I obtained in Lake Tanganyika there are 

 two highly interesting gastropods, which are sufficiently distinct from 

 all knoAvn forms to be worthy of at least generic rank. Such rank has 

 been accorded to them in a paper read before the Royal Society,^ in 

 which these two forms were figured and briefly described under the 

 names Batlianalia Howesi and Bythoceras iridescens. In two further 

 papers,* additional questions concerning the distribution of these 

 molluscs were considered, and the anatomy of Batlianalia, with 

 a short diagnosis, was given. Since, however, in these three papers 

 they were treated rather from a faunistic and an anatomical standpoint, 

 than from that of the systematist, it has been deemed advisable to 

 publish diagnoses of these genera in this journal, where they will 

 be more accessible for the conchologist. 



Both forms live only at very great depths, and were obtained from 

 the southern half of the lake ; they are essentially members of what 

 I have termed the halolimnic ^ fauna of Lake Tanganyika. 



1. Bathanalia Howesi, Moore. Fig. 11. 

 Batlianalia Sowed, Moore: Proc. Roy. Soc, vol. Ixii (March, 1898), 

 p. 452, fig. 2 ; Quart. Journ. Micro. Sci., vol. xli (March, 

 1898), p. 192, pi. xii, figs. 29-31 and 33. 



Shell conical, turreted ; colour transparent white, with a faint trace of 

 brownish periostracum upon the lirae ; whorls 8, apical whorls missing, 

 angular or carinated, the angulations being more acute in the upper 

 whorls, while in the last whorl the shell becomes slightly convex 

 both above and below the carina, carina from apex to mouth of shell 

 bearing numerous short spinous processes, whorls strongly sculptured 

 with numerous longitudinal spiral nodulous lirse, from 5-6 above 

 and 8-10 stronger ones below the carina; mouth rotund-pyriform, 

 last spine forming as a notch in the outer lip ; columella open ; 

 operculum littorinoid. 



Except in the possession of a more open columella, the genus 

 Batlianalia is conchologically indistinguishable from the Jurassic genus 

 Amherlya. 



Anatomically Batlianalia closely resembles the genus Typhohia, 

 but differs from it somewhat in its radula ^ and greatly in its shell ; 

 unlike the latter genus, the shells of Batlianalia are singularly devoid 

 of variation. 



Batlianalia was dredged living at a depth of 800 feet and upwards, 

 near Mleroes, Lake Tanganyika. 



1 Proc. Eoy. Soc. Lend., vol. Ixii (1898), p. 452. 



2 Quart. Journ. Micro. Sci., a^oI. xli (1898), pp. 159-202 and 303-320. 



•' aKs, 'salt,' and Ai/xj"?) 'lake.' ■* Quart. Journ. Micro. Sci., loc. cit., p. 189. 



