ISOPODS OF NORTH AMERICA. 



9 



one-half mm. wide; the anterior margin is somewhat triangularly 



produced, with apex very obtuse. The e} r es are small, composite, and 



situated at the antero-lateral angles of the head. 



The first pair of antennae have the basal article 



very long and about equal to two-thirds the 



length of the head; the second article is half as 



long as the first; the third is almost as long as 



the second; the terminal article is minute. The 



first pair of antennas are about 1 mm. in length. 



The second antennae have the first article long; 



the second article is about half as long as the 



first; the third is a little longer than the first; 



the fourth is half as long as the third; the fifth 



article is minute. The second antennae are 



more slender and are shorter than the first pair, 



extending only to the end of the second article 



of the first pair. The maxillipeds have a palp 



of four articles. The palp of the mandibles is 



wanting. 



The first segment of the thorax is united with the head to form a 

 carapace. The second and third segments are subequal, and each is a 

 little shorter than any of the four following, which are about equal in 

 length. 



The abdomen is composed of five segments, four anterior to the 

 terminal segment. The first two have a transverse row of long plu- 

 mose hairs fringing the posterior margins. The fourth segment is 



FIG. 11. TANAIS CAVOLINII 

 (AFTER HARGER). x 8. 



a b c d e f 



FIG. 12. TANAIS CAVOLINII. a, FIRST LEG. b, MAXILLIPED. c, FIRST ANTENNA, d, MANDIBLE. 

 e, UROPOD. /, SECOND ANTENNA. 



very short, not more than half as long as any of the three preceding 

 segments. The terminal segment has the posterior margin obtusely 

 pointed. The uropoda are composed of three articles, a basal article 

 or peduncle and two others, which form a single branch. The second 

 article of the single ramus is half as long as the first article. 



The first pair of legs are chelate; the other six pairs are ambulatory. 



There are three pairs of pleopoda. 



