AKT.B. NORTH AMERICAN PARASITIC COPEPODS WILSON. 27 



(p. 352) Tucca was shown to be an Ergasilid, and Norion is just as 

 certainly a Dichelesthiid. 



Nordmann did not find any traces of the swimming legs, but the 

 curved pads on the posterior margin of the cephalothorax are quite 

 manifestly the rudiments of the first pair of legs, and it is also possi- 

 ble, as Basset-Smith has suggested, that the divided ventral plate 

 may represent the remaining legs, but he was certainly wrong when 

 he stated that the anterior wing-like expansions belonged to the 

 ventral plate and that there were no dorsal plates. 



A revised diagnosis is here presented in order to call attention 

 again to this remarkable parasite and to offer certain corrections and 

 suggestions in reference to its morphology. 



The genus seems valid and corresponds well with Anthosoma, 

 Caetrodes, and Saguni. Accordingly we may accept it as far as it 

 has been described and await further information before finally 

 deciding upon its validity. 



Genus CAETRODES Wilson. 



Caetrodes Wilson, Report on the Pearl Oyster Fisheries of the Gulf of 

 Manaar, by W. A. Herdman, Supplementary Report No. 34, pt. 5, p. 203. 



GeneHc characters of feTnale. — Body regions distinct. Head cov- 

 ered with a dorsal carapace, which is obovate in shape, strongly 

 arched and considerably widened anteriorly, narrowed and flattened 

 posteriorly, where it projects back over the thorax segments but is 

 not attached to them. Frontal margin turned under the carapace, 

 carrying the base of the anterior antennae onto the ventral surface. 

 Five free thorax segments, indistinctly separated and diminishing in 

 width backwards, the fifth one sending back a wide lobe on either 

 side of the genital segment. The latter small, transversely oblong 

 and inclosed on. three sides by the fifth segment. Abdomen small, 

 hemispherical, one-jointed; anal laminae longer than the abdomen, 

 narrow, and terminating in a spine and a claw. 



First antennae five-jointed, slender, sparsely setose; second pair 

 stout, ending in a prehensile claw. First and second maxillae rudi- 

 mentary, uniramose, two- jointed, attached close beside the mouth 

 tube and about the same size. Maxillipeds slender, two- jointed. 

 Two pairs of biramose swimming legs close together at the anterior 

 end of the thorax; rami linear, two-jointed. Egg tubes longer than 

 the body, eggs large, not much flattened. Male unknown. 



Type of the genus. — Caetrodes pholas^ monotypic. 



Remarks. — This genus is at once distinguished by the claws on 

 the tips of the anal laminae, which assist the parasite in maintaining 

 its peculiar hold upon its host. So far as known no other copepod 

 is thus armed. 



