854 REPORT OP COMMISSIONER OF FISH AND FISHERIES. [136] 



Habitat. Tryyon centrura, stomach arid pylorus. August, 1884 and 

 1887. Wood's Holl, Massaclui setts. 



Upon four different occasions I have obtained a few Tetrarliyncld from 

 the stomach of the sting ray (Trygon centrura), which, with the some- 

 what hurried examination that was made of them while they were alive, 

 were supposed to belong to the same species. After an examination of 

 the alcoholic specimens, however, I find that there are two entirely dis- 

 tinct species in each of the four lots. These differ from each other most 

 in the character of the hooklets on the proboscides, T. tenue, having 

 minute spinose hooklets, while the hooklets of T. robustum are short, 

 stout, and strongly recurved. 



These parasites were found as follows : 



These specimens were all found either in the stomach proper or in 

 the pylorus. 



Of the following measurements No. 1 was a living specimen, the 

 others alcoholic : 



In No. 1 the diameter of neck at collar wns 0.1S 1 '" 11 ; length of neck 

 proper, 0.40 mni ; length of collar, 0.14 mm ; length of bothria, varying from 

 0.30 to 0.56 mm ; posterior segments, from 0.94 to 1.16 mm . 



In an alcoholic specimen, 13 mm in length, the length of the head and 

 neck was 0.78 mm ; in another, 17 ram in length, the length of the head and 

 neck was 0.48 mm . 



