THE CRUSTACEA OF NEW JERSEY. 97 



mo\'ement of the swimming-legs. Hence they can be kept ahve 

 but a very short time. As they are gregarious and gather to- 

 gether in colonies, whose combined lacerations form a deep pit 

 extending through the skin and into the flesh of their host, they 

 are kept alive after the skin of their host may have dried. Such 

 a pit does not dry as quickly as other portions of the surface of 

 the host's body, and the parasites, being fastened in its very 

 bottom, are not only protected from abrasion, but are also kept 

 moist long after the fish's skin has become dry and parched. 



Key to the genera. 



a. Females. Third dorsal plates of medium size, covering quite a portion of 



genital segment ; latter large as or larger than carapace, 



b. Abdomen without wings ; egg-strings long and entirely visible ; genital 



segment a little smaller than carapace; margins of carapace and 



dorsal plates finally toothed ; third dorsal plates covering three-fifths 



of genital segment ; rami of first swimming-legs normally developed. 



PHILORTHRAGORISCUS 



bb. Abdomen with broad wings between which and genital segment long 

 egg-strings are entirely concealed ; genital segment much larger than 

 carapace. 

 c. First antennse three-jointed, prominent; second pair projecting be- 

 yond carapace margin ; posterior border of carapace slightly con- 

 cave ; margin of carapace and dorsal plates coarsely toothed. 



ORTHAGORISCICOLA 



cc. First antennae two-jointed, not prominent; second antennae hidden; 



posterior border of carapace deeply concave ; margin of carapace 



and dorsal plates smooth. cecrops 



aa. Males. Third dorsal plates small, overlapping genital segment but little ; 



latter much smaller than carapace. 



d. Third dorsal plates very much reduced; grooving of carapace 

 distinct ; abdomen largely visible ; second antennae much en- 

 larged, projects beyond carapace; first dorsal plates large; 

 genital segment with large spines at posterior corners; first 

 swimming-legs normally developed. philorthragoriscus 



dd. Third dorsal plates relatively large as in female; grooving of 

 carapace nearly invisible; abdomen almost or quite concealed. 

 e. First antennae three-jointed; second and third thorax seg- 

 ments distinct and entirely visible, without plates; abdomen 

 partly visible; margins of plates on fourth and genital seg- 

 ments coarsely toothed. orthagoriscicola 

 ee. First antennae two-jointed; second and third thorax seg- 

 ments fused inter se and furnished with pair of broad 

 lateral plates, concealed beneath carapace ; abdoir.en also 

 entirely concealed. cecrops 



7 MU 



