286 s. GOTO. 



deferens, must be the vagina. The vitellaria are quite extensive 

 and are almost entirely confined to the lateral portions of the 

 body external to the intestine. 



Habitat. — On the body of a skate, above and below. 



Loc. — Off Cape Cod. From Prof. Verrill, to whom my best 

 thanks are due. 



Dionchus Agassizi n. g. n. sp. 

 (PL XXI, figs. 19-24.) 



The body is elongated, and the breadth gradually decreases 

 backwards. The total length is 2 mm. as measured on a some- 

 what contracted specimen. The anterior end is triangular, 

 with a pointed apex, and there is a shallow constriction just 

 behind the pharynx. The posterior end terminates in 

 an elliptical sucker, whose internal surface is divided into ten 

 areas by as many radial ridges, which do not quite reach the 

 centre of the sucker and thus leave here a circular depression 

 (fig. 20). When killed with a hot solution of corrosive subli- 

 mate, the whole body, but especially the posterior portion, 

 strongly curves towards the ventrum. This is due to the strong 

 development of the longitudinal muscular fibres of tlie ventral side ; 

 and even in specimens killed under the pressure of a cover-slip, 

 it is rare to prevent the curvature of the hind part of the body 

 and to obtain fully the ventral aspect of the sucker. The latter 

 is provided with one pair of strong hooks situated on either side 

 of the centre. Each hook consists of a flattened basal portion 

 and a recurved claw-like distal portion, and is hollow for the 

 greater part. The basal portion has a thick process on one 

 side. These hooks attach the worm so tenaciously to the sub- 

 stratum that the distal claw-like portion mostly breaks off in 



