ANATOMY OF PALUDESTRINA 165 



forwards into the pylorus. On the side of the stomach opposite 

 to the oesophageal and hepatic apertures the epithelium 

 gives rise to a dense cuticle which occupies the major part of 

 the posterior part of the stomach but diminishes anteriorly. 



Vitrei la and Bythinella apparently differ conspicu- 

 ously in the lining of the stomach. In the latter form only 

 a small part of the stomach is ciliated, while the contrary is 

 true of Vitrella. P. ventrosa is more or less inter- 

 mediate between the two in this respect. 



The base of the epithelium which secretes the cuticle is, as 

 in the case of the oral cuticle, rendered conspicuous by a layer 

 of densely-staining granules. The stomach is crossed by 

 numerous ridges of which the most constant and most conspicu- 

 ous is a large and strongly-developed one lying transversely 

 in the cavity above the hepatic duct. Grooves with specialized 

 cuticle are found in the neighbourhood of the latter. 



The style sac is blunt externally and rather thimble-shaped. 

 In transverse section it is circular and exhibits on the side 

 towards the pylorus a groove of characteristic structure. The 

 latter corresponds in its histological features to the similar 

 structure in Bythinella. Bregenzer has offered no explana- 

 tion of the function of this groove. Unfortunately the structure 

 and relationship of the style itself caimot be demonstrated in 

 fixed material. I am under the impression, however, that, 

 in the living animal, the style is not loose in its sac but attached. 

 If that is the case it may be secreted in the groove. 



The rest of the sac is simple, being composed of a thick 

 ciliated epithelium. The cilia are very dense and much longer 

 than the cells. 



No one familiar with the recent work on the style sac in 

 Lamellibranchia can fail to be struck with the similarity 

 between the structure here described and that figured by Nelson 

 (14) for Lampsilis anodontoides. In both forms the 

 pyloric part of the intestine communicates by a narrow slit 

 with the style sac, the walls of which are composed of a single 

 layer of columnar ciliated cells. In Lampsilis the resem- 

 blance to Paludestrina is still more emphasized by the 



