[29] 



ENTOZOA OF MARINE FISHES OF NEW ENGLAND. 



481 



The following measurements of head and neck give proportions which 

 hold good for all : 



Dimensions. 



Length of head 



Breadth of head 



Length of neck 



Breadth of neck, anterior 



Breadth of neck, posterior 



Breadth of strobile back of neck 



Marginal 

 view. 



mm. 



0.90 

 1.10 

 0.7C 

 0.72 

 0.40 

 0.28 



Lateral 

 view. 



mm. 

 1.04 

 1.04 



0.70 

 0.7G 

 0.44 

 0.28 



Millimeters. 



Length of proboscis 0. 840 



Breadth of proboscis, exclusive of projecting hooks 0. 043 



Breadth of proboscis, inclusive of projecting hooks ..:. 0. 078 



Length of anterior hooks 0. 023 



Breadth of base of anterior hooks 0. 013 



Length of hooks on base of proboscis 0.014 



Breadth of base of hooks on base of proboscis 0. Oil 



In the summer of 1884 I obtained two lots of these worms from the 

 alimentary tract of the Dusky Shark (Carcharias obscurus). 



The first lot, containing approximately 200 individuals, was lodged 

 iu the pyloric portion of the stomach, where the worms were so massed 

 together as to make a swelling in the pylorus which was discernible 

 before opening. 



These specimens were not studied closely while they were alive. 

 Upon examining them subsequently as alcoholic specimens, it was 

 found that there was a very considerable variation in the length of the 

 strobiles, and to some extent iu the proportions of the segments. In 

 the foregoing description I have enumerated those characters which 

 belong to all ; but inasmuch as there are some more or less clearly 

 marked groups among them I shall add some further observations. I 

 deem this of importance, for the reason that, if it were not for the 

 great number of intermediate forms which these two lots furnish, one 

 might be justified in making two, if not three, distinct species instead 

 of one. The second lot came from the pylorus and spiral intestine of 

 the same species of shark (C. obscurus). 



Three groups w T ere observed iu the first lot. These differ from each 

 other principally in the shape and proportions of the segments, the 

 distance from the head at which mature proglottides occur, and in the 

 total length of the strobile. 



In the first group, Which, for" the sake of clearness, I shall name var. a 

 (Plate IV, Figs. 9-12), the mature proglottides are flat and thin, square, 

 or the posterior ones a little broader than long. When there are but 

 few mature proglottides they increase iu breadth rather abruptly, so 

 that the strobile has a somewhat club-shaped or linear-obovate out- 

 line. 



S. Mis. 90 31 



