192 J. E. S. MOORE. 



to be unquestionably the labial commissure described by 

 Bouvier as characteristic of a number of the Archi-tsenio- 

 glossate and Rhipidoglossate types. 



The cerebro-pedal connectives are very long (PI. 20, figs. 7 

 and 10), and altogether the length of the cerebro-pleural, cere- 

 bro-pedal, and pleuro- pedal connectives gives to the nervous 

 system the longi-commissurate character described by Haller. 



The pedal ganglia are united by a rather small connection, 

 and are prolonged into the foot along the course of two well- 

 developed scalariform pedal cords. Between these pedal cords 

 there exist ladder-like connections similar to those found betwe&n 

 the pedal cords of Cyclopherus. 



The otocysts in Nassopsis are relatively immense (PI. 20, 

 figs. 7 and 10, ot.). They are situated well up on the course 

 of the pedo-pleural connectives, and the otocyst nerves pass 

 obliquely from them towards the cerebral ganglia, and are 

 not quite correctly indicated in figs. 7 and 10. The otoliths 

 are small, numerous, and rectangular, with the faces slightly 

 convex (fig. 10). 



The reproductive apparatus in Nassopsis is similar in 

 many ways to tliat of Ty phobia, both male and female appa- 

 ratus occupying the same general position. In the male the 

 genital gland occupies the u[)per surface of the apical whorl in 

 the body, and is connected by several channels with a nearly 

 straight vas deferens, represented in PI. 21, fig. 2, v. d. This 

 latter structure opens without any modifications along its 

 course by the slit-like aperture represented in PI. 21, fig. 5. 

 In the female the ovary occupies the same position as the male 

 gland, and in like manner it is connected with the nearly 

 straight oviduct, the lower portion of which, or that which lies 

 within the mantle cavity, forming a brood-chamber where the 

 eggs go through their later stages of development (PI. 20, 

 fig. 6,6.5.). 



(b) Bythoceras. 



Like Nassopsis, the genus Bythoceras, so far as is at 

 present known, is exclusively restricted to Tanganyika, and as a 



