ISOPODS OF NORTH AMERICA. 33 



taken together; the anterior margin terminates in the middle line in a 

 very short, blunt rostrum; on either side of the shallow excavations 

 which lodge the basal joints of the antennules are the minute but sep- 

 arate ocular lobes; these are rounded, oval in front, the anterior end 

 being pointed and prolonged; there is no trace of any ocular structures. 

 The first free thoracic segment is shorter, rather more than half the 

 length of the four succeeding segments, which are subequal; the last 

 thoracic segment is shorter than the foregoing; each of these segments 

 is rather narrower anteriorly where it articulates with the segment in 

 front; the general shape of the segment is short, oblong, with rounded 

 angles; this does not apply to the first-or to the last free segment of 

 the thorax, which are broader than they are long. 



"The five anterior segments of the abdomen are equal in length and 

 in diameter, only the first one being a trifle longer than the rest. 



"The terminal segment of the abdomen is longer and wider than the 

 rest; it has a pair of lateral projections with which the uropoda articu- 

 late; posteriorly it is rounded and a minute median triangular process 

 projects from the extremity; on either side of this the posterior mar- 

 gin of the abdomen is slightly concave. 



"The antennules are considerably stouter than the antennae; the 

 peduncle has three joints, of which the proximal one is much the long- 

 est and stoutest; it is furnished with a tuft (three or four) of slender 

 spines on the outer side, near to its articulation with the second joint; 

 the second joint is about one-fourth of the length of the first^ and like 

 it has a tuft of slender spines occupying a similar position to those of 

 the basal joint, and one slender hair-like spine upon the opposite side; 

 the third joint of the peduncle is stouter again, with one or two short 

 slender spines upon the inner as well as the outer margin just before 

 its articulation with the flagellum; the latter consists of four joints, 

 of which the first is very much the longest, as well as broader than the 

 succeeding joints; each of the three distal joints is furnished with a 

 single olfactory hair. 



"The antennas are considerably more slender and shorter than the 

 antennules; the peduncle consistsof five joints; the basal joint is short 

 and oval, much stouter than any of the succeeding joints, which are of 

 equal thickness; the second joint is moderately long, the third stouter, 

 the fourth and fifth subequal to each other and to the second joint; 

 the flagellum has four joints which decrease gradually in diameter, the 

 first being the widest; the first joint of the flagellum is also the long- 

 est, the two middle ones are shorter and subequal, the fourth shorter 

 still and provided at its extremity with a tuft of fine hairs. 



"As the only specimen was mounted on a slide in Canada balsam it 

 is impossible to describe in a detailed manner the mouth appendages, 

 which do not appear, as far as could be seen, to present any marked 

 differences from those of other species. 

 2858905 3 



