[99] NOTES ON ENTOZOA OF MARINE FISHES. 817 



as the shorter prong. Tliey join by a simple articulation. In front of 

 each pair of hooks is a triangular pad which bears a 1 single, circular, 

 supplemental disk. The neck is rather long and merges imperceptibly 

 into the segmented body. The first segments are broader than long, 

 but increase in length uniformly. The median segments are squarish, 

 posterior segments longer than broad, slightly irregular in outline. In 

 all specimens thus far observed the posterior segments are from four 

 to eight times as long as broad. In most of the specimens, especially 

 the shorter ones, the last segment is attenuated at the posterior end. 



Genital openings marginal, near the middle of the segment. Cirrus 

 very long when fully extended, bulbous at base when partly everted, 

 densely echinatc. Length, maximum 20""". 



Habitat Tnjgon cenlrura, spiral valve, July, 1886 ; August, 1887. 

 Wood's Holl, Massachusetts. 



I have obtained this parasite on four different occasions from the 

 spiral valve of the sting ray (Trygon centrum^. Following is a brief 

 summary of the different captures : 



July 29, 1886 ; about thirty specimens from spiral valve of one ray. longest speci- 

 men about 20 mm . 



August 1, 1887; four specimens obtained from a lot of three rays; longest speci- 

 men about 9 mm . 



August 8, 1887 ; about two hundred and fourteen specimens ; all quite small ; max- 

 imum about 5""", from a single ray. 



August 10, 1887; live specimens; maximum 13.5 mm , from two rays. Three of these 

 specimens, maximum 13.5 mm , had black hooks. The remaining two, maximum 6 mm , 

 had the ordinary amber-colored hooks. The black color, however, disappeared from 

 the former when the specimens were placed in alcohol. 



The following measurements, with the exception of the hooks of one 

 or two specimens, were made from living specimens : 



There is some difference between the larger specimens, 15 to 20 mm in 

 length, and the smaller specimens, 4 to 6 mm in length, besides a differ- 

 ence in size. This difference, however, is confined to the region of the 

 posterior segments, where considerable variety is to be expected in 

 H. Mis. 13352 



