NO. 2063. NORTH AMERICAN PARASITIC C0PEP0D8— WILSON. 683 



gins almost squarely truncated ; posterior body made up of four seg- 

 ments of the same width, but the fost and third are considerably 

 shorter than the second and fourth (fig. 13, p. 593). 



First antennae attached to the anterior corners of the carapace on 

 the dorsal surface, three-jointed, the terminal joint as long as the 

 basal ones. These antennae are turned back and approximated close 

 to the sides of the carapace; the basal joint is armed with a single 

 small spine, the terminal joint ends in a tuft of six spines, uaiequal 

 in length. The second antennae project diagonally forward from 

 beneath the bases of the first pair; they are two-jointed, the terminal 

 joint being a stout acuminate claw, bent into a half circle and armed 

 at its base on the ventral surface with a short spine. The mouth 

 tube is cylindrical, of the same diameter throughout, and bluntly 

 rounded at the tip. The mandibles are included in the tube and reach 

 to its tip; they are slender, slightly enlarged at both ends, and fur- 

 nished with a dozen small saw teeth, all about the same size. 



Inside the base of the mandibles can be seen the tips of the new 

 pair which are to appear at the next molt. 



The fii-st maxillae are attached to the ventral surface of the head, 

 outside of and close to the base of the mouth tube. Each is com- 

 posed of two rami of the same length, the exopod being stout and 

 conical and ending in a single spine, the endopod slender and cyhn- 

 drical and ending in two long equal spines (fig. 14, p. 594). 



The second maxillae are two-jointed, the basal joint longer and 

 stouter than the terminal joint; they end in a blunt claw which is 

 bent strongly near the base. The maxilhpeds are longer and more 

 slender than the second maxillae, the basal joint much stouter than 

 the terminal; the latter ends in a slender, acuminate claw, only 

 slightly bent, with a small spine on the ventral surface at its base. 

 Both pairs of legs are biramose, the rami one-jointed; the basal joints 

 carry a long threadlike spine on the outer margin; the exopods are 

 armed with two long and two short spines on the outer margin, the 

 latter fringed with fine teeth, and four plumose setae at the tip; the 

 endopods have a single small spine at the outer distal corner and six 

 plumose setae, one of which is removed from the other five and ap- 

 pears on the inner margin close to the base. 



Remarks. — This is the oldest species, and therefore an appropriate 

 type of the genus. Its history has already been given under the 

 genus remarks (see p. 667). It is so common that it has been at least 

 mentioned by almost everyone who has dealt with the parasitic 

 copepods. And yet it is surprising to find that it has never been 

 described in any detail, while the best figures that have been pub- 

 lished are either too small to show the detail (Kr0yer, 1837), are 

 taken at such an angle as to give a poor idea of the real structure 

 (Vogt, 1877), or are buried in a general treatise (Claus, 1861) 



