426 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



Unfortunately, the name Hersilia had been twice preoccupied, once 

 in 1816 by Savigny for an Arachnid genus and again in 1834 by 

 Dejean for a genus of Coleoptera. Consequently it can not stand for 

 a copepod genus, and we must accept Kossmann's generic name Clau- 

 sidium and the specific name apodiforme given by Philippi. With 

 the suppression of the name Hersilia the family name Hersiliidae 

 must also be dropped, and Clausidiidae substituted in its place 

 as has already been done by Sars. 1 



The family is chiefly characterized, as Sars stated, "by the non- 

 prehensile posterior antennae, the form of the anterior lip, the peculiar 

 armature of the maxillae, and partly also by the structure of the 

 maxillipeds." 2 The genus Clausidium may be thus diagnosed. 



External generic characters of female. — General form short, broad, 

 and strongly flattened; first thorax segment fused with the head, 

 second and third segments free, fourth and fifth segments fused, and 

 covered with a single plate. No eyes visible. Genital segment of 

 varying length, abdomen three-jointed; egg strings very short, eggs 

 multiseriate. First antennae seven-jointed, setose; second antennae 

 nonprehensile, tipped with long setae ; mandibles bearing a tooth and 

 a tuft of hair; first maxillae knoblike, armed with short spines; second 

 maxillae biramose, the endopod a bipartite spine, the exopod one or 

 more plumose setae; maxillipeds with stout basal joints and small 

 terminal joint, tipped with plumose setae. First four pairs of legs 

 biramose, the endopods armed with sucking disks, the first pair still 

 further modified for prehension; fifth pair uniramose, flattened. 



External generic characters of male. — General form elongate, slender, 

 much smaller than the female. Second, third, and fourth segments 

 free, the dorsal plate on the latter covering the base of the fifth 

 segment. 



Genital segment with rudimentary sixth legs on the lateral mar- 

 gins. Abdomen three-jointed. Appendages like those of the 

 female except the maxillipeds, which are two-jointed and armed 

 with teeth and spines. 



Characteristic habit of the genus. — The male and female are fastened 

 together in 90 per cent of the adult specimens obtained. The male 

 clings to the abdomen of the female by means of his maxillipeds and 

 first legs, with his dorsal surface in the same direction as hers, and 

 this adherence is maintained even in alcohol and preservatives. 



Type of the genus. — Clausidium apodiforme (Philippi), monotypic. 



KEY TO THE SPECIES. 



1. Genital segment with rudimentary sixth legs on its lateral margins; maxillipeds 

 two-jointed and tipped with spines and teeth, males 2. 



1. Genital segment with smooth lateral margins; maxillipeds four-jointed and tipped 

 with long plumose setae, females 3. 



1 Crustacea of Norway, vol. 6, pt. 11, 1917, Copepoda Cyclopoida, p. 144. 

 • Idem, footnote. 



