170 GUY C. ROBSON 



the same form Bregenzer notes no special differentiation of 

 the outer cornea from the adjacent epithehum of the tentacle 

 base. This is not the case in P . v e n t r o s a , in which the 

 external cornea is always noticeably thinner. 



The osph radium, as in Vitrei la and Bythinella, 

 is a simple ridge-like elevation on the left-hand side of the 

 gill close to the junction of the roof of the pallial cavity with 

 its floor. There are no foliations such as occur in some other 

 Taenioglossa. The laterally-disposed pigment cells contain 

 brownish pigment granules. The ciliated and sensory layer 

 overlies a large and elongate osphradial ganglion. 



4. The Eespiratory and Circulatory System. 



(1) Pericardium and Heart (Text-fig. 5). 



The pericardium lies on the posterior side of the body- 

 whorl in a superficial position covered only by the body- 

 epithelium. It is placed at the posterior end of the pallial 

 cavity on the left-hand side, and is roughly bounded by the 

 kidney and the extremity of the style sac. 



No trace of a reno-pericardial orifice could be found. Seibold 

 was unable to find one in V i t r e 1 1 a ; nor is it referred to by 

 Bregenzer for Bythinella. It occurs in both Cyclo- 

 stoma (8) and Valvata (1). The auricle was never found 

 in an expanded condition, so that its general structure cannot 

 be defined. The ventricle is, as usual, thick-walled and 

 muscular, though a thinner-walled portion of varying extent 

 is invariably to be seen. 



(2) Vascular System. 



The descriptions of this system in other Taenioglossa are 

 very unsatisfactory. The accounts given are usually incom- 

 plete, and frequently omit some portion from consideration. 

 It may also be pointed out that on one point at least two of 

 the most up-to-date treatises on the Mollusca are at variance. 

 Lang (11, p. 322) says, ' Bald offnen sich die Arterien ... in 

 arterielle Sinusse. Unter diesen verdient besonders der 

 grosse Kopfsinus . . .' Pelseneer (15), who alludes to the 



