ISOPODS OF NORTH AMERICA. 



341 



article; the fourth article is one and a half times longer than the first 

 article. The first antenna; extend to the end of the second article of 

 the peduncle of the second antenna?. The basal 

 article of the second antennae is short, and, on 

 the dorsal side, does not extend beyond the 

 antero-lateral angles of the head; .the second 

 article extends to the end of the first pair of 

 antennae; the third article is nearly three times 

 as long as the second; the fourth and fifth are 

 subequal, and each is one and a half times 

 longer than the third. The flagellum is com- 

 posed of ten articles, the last article termina- 

 ting in a short spine. The second antennae are 

 a little longer than the body, being 37 mm. in 

 length. The maxilliped has a palp of five arti- 

 cles. The palp of the mandibles is wanting. 



The first three segments of the thorax are 

 subequal; the fourth is twice as long as any of 

 the preceding ones; the fifth is about half as 

 long as the fourth; the sixth and seventh are a 

 little shorter than the fifth. The last three 

 segments are each furnished with two low 

 tubercles, one on either side of the median 

 longitudinal line. The lateral parts of the first 

 segment are expanded and surround the pos- 

 terior portion of the head. The epimera on 

 the second, third, and fourth segments are small, narrow plates, dis- 

 tinctly separated from the segments and placed on the antero-lateral 

 angles; they are not visible in a dorsal view. The 

 epimera of the last three segments are distinctly sep- 

 arated from the segments and are visible in a dorsal 

 view; they are large, broad plates with the exterior 

 angles bluntly rounded. 



The first two segments of the abdomen are short, 

 and each is provided with two low tubercles, one on 

 either side of the median longitudinal line. The 

 terminal segment is long, and produced to an ex- 

 tremity which is somewhat acute. About the middle 

 of the segment, on the dorsal surface, are two low 

 longitudinal ridges, one on either side of the median 

 line. There is also at the base of the segment a 

 blunt projection, almost inconspicuous, on either 

 side of the lateral margin. 

 The first four pairs of legs are slender, directed forward, and 

 densely covered with long., slender hairs on the inferior margins of all 

 the articles. The first pair are much shorter than the three following 



FIG. 369. ARCTURTJS BAFFINT 

 VAE. TUBEROSU& (AFTER 

 BENEDICT), x 1J. 



FIG. 370. ARCTURUS 

 BAFFINI VAR. TUBER- 

 osus. MAXILLIPED. 

 x 15}. 



