NO. 2194. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 65 



ond antennae one- jointed, the joint long and conical and furnished 

 on the inner margin with a cup-shaped socket, into which the tip of 

 the stout and strongly curved terminal claw shuts, forming a chela. 

 Proboscis long and narrow and parallel with the body axis in con- 

 sequence of the turning forward of the head ; it is shorter and much 

 narrower than in radiahis, and is not constricted at the center. It 

 terminates similarly in a pair of large dorso-lateral lobes and a sub- 

 quadrangular plate, from under whose base project the maxillae. 

 These are t^Yo-jointed, the basal joint the stouter and the longer, and 

 armed on its anterior margin near the center with a short spine. 



The terminal joint is much shorter and narrower and is somewhat 

 enlarged at the distal end, to which is hinged the short and strongly 

 curved chiw. First two pairs of swimming legs with triangular 

 basal plates carrying two rudimentary rami; third pair with an ellip- 

 tical basal plate, reduced in size and carrying but one ranms; fourth 

 pair with an elliptical basal plate, still further reduced and with- 

 out any ramus. 



The anal laminae are greatly reduced in size also, and consist of 

 tiny knobs, one on either side of the anus, and destitute of setae. 

 Color (preserved material), a uniform orange yellow; the head, 

 neck, and egg strings brownish, the body often spotted with brown. 



Total length without egg strings, 20 to 30 mm. Length of trunk, 

 12 to 18 mm. ; diameter, 1.50 mm. Length of egg strings, 15 to 20 mm. 

 (afixus, fastened or attached, that is, to a bone.) 

 Remarks. — This species seems to be a parasite chiefly of the tomcod, 

 which it often infests in great numbers (see tables, p. 12). Its favor- 

 ite point of attachment is on the isthmus of the fish's throat, be- 

 tween the opercula, but it is also often found along the ventral mar- 

 gins of the opercula. It can I'C readily recognized by the fact that 

 it is always attached by the front of the head to a bone, and this 

 one character will separate it from radiatus when, as often happens, 

 the two are found together upon the same fish. Further distinctions 

 are the attachment lamellae, the forward flexure of the cephalothorax, 

 and the very short horns, only two in number. From pohjceraus^ 

 which also possesses attachment lamellae and a forward flexure of 

 the head, it may be distinguished by its larger size, by the relatively 

 longer and narrower trunk, and by the one pair of unbranched horns 

 instead of two pairs of branched ones. 



The bunching of this parasite on the throat of the tomcod is re- 

 markable, three or four of them often using the same opening through 

 the skin of the fish, but attaching themselves to different bones and 

 showing great differences in both the direction and amount of tor- 

 sion (see p. 15). 



77403 — Proc.N.M.vol.53— 17 5 



