AKT. 5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 85 



pod which he doubtfully referred to the genus Cycnus. He had but a 

 single specimen, which had been in alcohol for 40 years, and he was 

 hence unable to give many of the structural details. As we have 

 already seen, the name Cycnus was preoccupied (see p. 58), and so 

 this species can not retain that name, but it certainly does not belong 

 to the genus C ongericola^ to which the true Cyonus species have been 

 transferred. In size and general structure it corresponds well with 

 the present genus, but it can not be definitely located until further 

 details can be secured. 



Genus DICHELESTHIUM Hermann. 



C aligns, part Abildgaard, Skrivter af Naturhistorie Selskabet, vol. 3, 1794, 



p. 52. 

 Dichelesthium Hermann, Memoire Apterologique, 1804, p. 125. 

 Dichelestium Latkeille, Regne Animal de Cuvier, 1829, vol. 4, p. 200. 

 Dichelestium Milne Edv?ards, Histoire Naturelle des Crustac6s, 1840, vol. 3, 



p. 485. 

 Dichelesthium M. J. Rathbun, Fauna of New England, No. 5, Crustacea. 



1905, p. 97. 

 Dichelesthium Brian, Copepodi Parassiti dei Pesci d'ltalia. 1906, p. 67. 



External generic characters of female. — Head fused with the first 

 segment to form an angular cephalothorax ; four free thorax seg- 

 ments without dorsal plates or processes, but the second and third 

 segments are produced into lateral lobes. Genital segment oblong, 

 narrower than the free segments and tapered posteriorly; abdomen 

 small and one-jointed, attached to the ventral surface of the genital 

 segment. First antennae eight-jointed, with scattered setae; second 

 antennae large, cheliform, projecting in front of the head. 



Mandibles stylet-shaped, toothed at the tip ; first maxillae biramose,^ 

 the exopod much larger than the endopod; second maxillae two- 

 jointed and tipped with a small claw, sharp spines, and tufts of 

 hair; maxillipeds stout, uncinate. 



First two pairs of swimming legs biramose, the rami one-jointed; 

 third legs flattened uniramose laminae, one-jointed ; fourth and fifth 

 legs wanting. 



Egg strings slender, much longer than the body and straight, eggs 

 strongly flattened. 



External generic characters of male. — General body form the same 

 as that of the female; head relatively larger, its lateral margins 

 more angular. Only three free thorax segments, diminishing regu- 

 larly in size; fifth and genital segments completely fused, narrow, 

 and short; abdomen one-jointed. 



Antennae, mouth parts, and swimming legs like those of the female, 

 except that in the second legs the endopod is short and wide and 

 bears two spines and a wide flattened plate, and the third legs arc 

 relatively shorter and broader. 



