ANATOMY OF PALUDESTRINA 163 



excellent description given by Bregenzer for B y t h i n e 1 1 a . 

 They are two somewhat piriform bodies, united dorsally and 

 in the median line. They are rather flattened dorso-ventrally. 

 Posteriorly they diverge somewhat. Bregenzer states that in 

 Bythinella they are each divided into a ' Haupt-Knorpel ' and 

 a ' Knorpelspange ', and regards the difference between 

 Paludestrina and Bythinella in this respect as of taxo- 

 nomic value. Certainly no such division is apparent in Palu- 

 destrina ulvae and ventrosa. Lateral expansions 

 (' Fltigel ') observed in Bythinella occur in P . ventrosa 

 as well. 



The tissue of the cartilages is composed of irregular polygonal 

 cells with relatively small nuclei and a large amount of granular 

 pigment. 



It should be noted that Eougemont (18) states that in 

 Hydrobia sp. the cartilages are capable of movement upon 

 each other, if pressed downwards. In Paludestrina, Vitrella, 

 and Bythinella, this is, of course, quite possible ; as they 

 are no doubt very elastic and have a certain amount of ' play ' 

 on each other. 



The radula has been described and figured by Woodward 

 (24). 



The salivary glands are two in number. In P. ulvae 

 Henking describes two pairs with separate openings. Those 

 of P. ventrosa appear to correspond with Henking's first 

 (larger) pair. They run as far back as do the second pair 

 of P. ulvae and sometimes cross over in a similar 

 fashion. 



The lateral diverticula of the pharynx disappear posteriorly, 

 and the oesophagus develops a fresh series of diverticula in the 

 form of deep longitudinal furrows. Behind the cerebral com- 

 missure the oesophagus in most cases shows a tripartite arrange- 

 ment as in B y t h i n e 1 1 a . It is ciliated almost up to its distal 

 extremity. The stomach (Text-fig. 3) is an irregularly- 

 shaped organ with a forked appearance exteriorly due to the 

 fact that the intestine and style-sac leave the stomach parallel 

 to each other from its anterior end. The oesophagus and 



