196 J. B. S. MOORE. 



surface of the last two whorls of the animal's body. This 

 gland is put into connection with a large non-convoluted 

 oviduct or vas deferens, as the case may be, by a number of 

 fine tubes; and both duets pass beneath the intestine and open 

 just behind the anus in a large slit (PL 21, figs. 5 and 13, </. a.). 

 The genital duct in both sexes is much enlarged within the 

 mantle cavity, somewhat in the manner of the same structure 

 in the genus Typhobia. But in Bythoceras it is quite 

 destitute of the singular organ which I described as an evertible 

 penis in the male Typhobia.^ 



Comparative. 



In considering the phylogenetic relationships of Nassopsis 

 and By thoceras, it will be needless after the foregoing descrip- 

 tion to insist further upon the fact that these genera bear no 

 relation whatever to each other. Taking Nassopsis first, it 

 will have already been clearly seen that the characters of this 

 singular genus place it unquestionably among the archi-tsenio- 

 glossate forms. Whatever opinion one may hold as to the 

 value of the characters of the radula, it will have been seen that 

 they too place it among the more primitive portion of the great 

 melano-planaxoid group ; and beyond this it is doubtful whether 

 the radula can be used in a diagnostic sense at all. The large 

 buccal mass, long radular sac, and the characters of the salivary 

 glands certainly recall the littorinoid group, and at once dis- 

 sociate Nassopsis from the early Stromboid or Xenophoran 

 type to which Typhobia, Bathunalia, and Tanganyikia 

 all appear to bear more or less distinct affinities. The ex- 

 tremely archaic and simple condition of the whole digestive 

 tract in Nassopsis requires particular attention, for it will 

 have been seen by any one acquainted with my former accounts 

 of the anatomy of Typhobia, Tanganyikia, Bythoceras, 

 and even Spekia, that the digestive apparatus, and especially 

 the stomachic portion of the digestive apparatus in all these 

 molluscs is built upon the same general plan. They all possess 



' 'Quart. Jouni, Micr. Sci.,' vol. il, 1898, p. 191, luc. cit. 



