Anatomy and Affinities of Ilypsobia nosopliora. 403 



resembles that found in the PaludestriniJoe. The mandibles, 

 tlie epithelium wliich secretes the oral cuticle, and the two 

 lateral diverticula of the mouth are in general like those of 

 Paludestrina jenldnsi i^ii) or ventrosa (^12). The mandibles 

 consist of seventeen to twenty-one columnar pieces of 

 specialized cuticle. 



The secretory epithelium is continuous with that of the 

 pharynx. 



Posteriorly to the mandibles the mouth widens out and is 

 flattened over the oral cartila^-es. It shows the tripartite 

 arrangement seen in other Paludestrinids. The median 

 portion has a thin non-ciliated roof, and the lateral portions dip 

 down beside the cartilages. 



The salivary glands^ of which there is a single pair, open 

 into the lateral divisions just behind the level of the radula 

 and cartilages. They come into intimate connection with 

 each other across the oesophagus ; but it is doubtful whether 

 actual organic fusion occurs. 



The buccal carlihiges are symmetrical and joined in the 

 median line. Laterally they are somewhat flanged upwards, 

 while posteriorly they are divergent. 



The radula has been described elsewhere (10), while that 

 of H. humida was figured by Heude (5). In the material 

 forwarded by Dr. Cort there was a tendency for the animals 

 to show one less denticnlation on the two outer teeth than is 

 shown in the original description of H. nosophora. 



The stomach corresponds in its general structure with that 

 of other Paludestrinida:^, though the apertures of the oeso- 

 jdiagus and hepato-pancreas are not so close together as in 

 Paludestrina. The point of entrance of the oesophagus was 

 rather variable in the individuals examined. The cuticular 

 lining, the marked transverse ridge of the upper portion of 

 the stomach, and the position and structure of the style-sac 

 are remarkably similar to the condition seen in Paludestrina. 

 The comnninication between the pylorus and style-sac charac- 

 teristic of the latter genus is also found in Hypsohia. The 

 layer of dark pigment-granules in the stomach epithelium of 

 Paludestrina and Bythinella (3, 12) was not found in this 

 genus, though its absence may be due to accidental causes. 



The intestine exhibits a typhlosole. The rest of the 

 alimentary and digestive system does not call for special 

 comment. 



II. The Respiratory System. 



The character of the gill constitutes the most remarkable 

 feature in the structure of this animal, and differentiates 



2G^ 



