14 RESEARCHES UPON THE HYDROBIIN^ 



The generative organ of the male (Fig. 5) is of moderate size, 

 and situated on the right side of the back, a short distance behind 

 the right tentacle. It consists of a subglobular 

 base from which arise two forks or processes, 

 '^* * one of which is short, straight and flattened, 



with parallel sides and truncated extremity ; 

 while the other is longer, pointed, and coiled 

 loosely around the first, scarcely however com- 

 pleting a single turn. The generative orifice 

 in the female is in the usual position at the 

 juncture of the body with the mantle, a short 

 distance within the margin of the latter. 



The apparatus for taking food is as follows : At the inferior 

 end of the proboscis we find the mouth, with its jaws, which are 

 strong, and of the usual imbricated structure, resembling much 

 those of Bissoa, as figured by Troschel, except that the marginal 

 denticles are less pointed. The teeth of the lingual ribbon (Fig. 

 6) are arranged in seven rows, 3.1.3. The rhachidiau tooth is 



Fig. 6. 



very broad, at least three times as broad as long. It has a tongue- 

 shaped process arising at the centre of its concave anterior sur- 

 face, and projecting downward, reaching beyond the base. Its 

 lateral lobes are acutely triangular and somewhat curved, and 

 each of them presents, upon the anterior surface, a row of four 

 denticles, extending from near the cusp to the lateral extremity, 

 of which four denticles the two middle ones are minute, and the 



are meant, but these are not pectinated. These branchije are undoubt- 

 edly in a single row. 



In speaking of the gill, the larger or principal one is always referred 

 to in the present paper, the other being minute and inconspicuous, and 

 rarely mentioned in descriptions. 



