166 GUY C. ROBSON 



presence of a large mass of deeply-staining cells near the slit. 

 In several figures given by Nelson and Edmondson (7) we find 

 a lateral groove like that of Bythinella and Paludes- 

 t r i n a . The similarity between the crystalline style of Gastro- 

 pods and Lamelhbranchs has been commented upon by various 

 authors, and a short discussion may be found in Moore (12). 



The pylorus is ciliated and passes gradually into the 

 intestine proper. This follows the usual course. It is ciliated 

 almost to its extremity; a well-marked typhlosole is 

 found extending for some distance down the intestine. This 

 is apparently absent in Vitrella and Bythinella. 



The hepato-pancreas occupies the apical whorls as 

 usual, and consists of branching finger-like processes. The 

 duct is very short and fairly wide. No definite differentiation 

 of the liver-cells into granular- and ferment-cells with different 

 staining and contents could be made out. Vacuoles with 

 inclusions are seen in the plasma of the liver-cells. 



The rectum, when viewed transversely, exhibits a number 

 of longitudinal folds. It runs forward in the roof of the 

 pallial cavity projecting from the latter and ultimately becomes 

 free for a short distance. 



2. The Nervous System (Text-fig. 4). 



The only description of the nervous system of Paludes- 

 trina is that of Henking, which is insufficient and leaves 

 a good deal to be desired. 



The cerebral ganglia of P. ventrosa are long and rather 

 pointed anteriorly. The cerebro-pedal commissure is normal 

 though very short. The buccal commissure calls for some 

 comment as it is extremely short and thus unlike the elongate 

 form found in this and allied families. The buccal ganglia 

 are closely applied to the anterior end of the cerebral gangha. 

 In one or two cases very short connectives were found ; but 

 such instances are rare. Henking does not refer to the buccal 

 commissure as such in P. ulvae; but from his description 

 and figure the connectives would appear to be as short as in 

 P . ventrosa. 



