ISOPODS OF NORTH AMERICA. 



345 



dinal line, the two center ones beiiif^ the longest, ulthouo-h all are very 

 lono-. The fourth segment is twice as long as any of the other seg- 

 nictits, and has a transverse constriction on the posteriijr half of the 

 segment. On the anterior portion are six spines, three on either side 

 of the median line, the four outer ones being in a straight line, the 

 inner two below this line. On the posterior portion are six spines 

 also, three on either side of the median line. The fifth thoracic seg- 

 ment has twelve spines, six on eitluM- side of the median line. The 

 sixth segment has ten spines, 

 live on either side. The se\'- 

 enth and last segment has 

 eight spines, four on either 

 side. 



The abdomen is composed 

 of two segments. The tirstis 

 short, with twelve spines, six 

 on either side of the median 

 line, the four inner ones being- 

 arranged in two longitudinal 

 series, the two upper ones 

 being small, the two lower 

 ones very long. The termi- 

 nal segment has the upper 

 surface smooth. This seg- 

 ment terminates in two long 

 divergent spines. There is a 

 single spine on the lateral 

 margin' on either side abo,ut 

 th(> middle of the segment, 

 and another near the base of 

 the segment. The three anterior pairs of legs have each two spines 

 on the coxal joint and one spine on the basis. The bod}' increases in 

 width from the tirstto the fourth segment, and then decreases in width 

 from the fourth to the tei-minal segment. 



One specimen from iM'ska Harbor, Aleutian Islands, 10 fathoms, 

 collected by Dr. W. H. Dall. 



7//7V.— Cat. No. 225S1, U.S.N.M. 



This species differs from P. murdochi in the absence of spines on the 

 third joint of the second pair of antenna?; in the greater length of this 

 joint in relation to the preceding joint; in the greater length of the two 

 following joints; in the presence of a single spine on the anterior part 

 of the head, while in 1\ uiurdoch! thdvo, are three, and of two spines on 

 the posterior part, while in /*. murdoch! there are four; in the absence 

 of two small spines just below the constriction in the fourth segment; 

 in the absence of the row of spines on the terminal segment of the 

 body; and in the presence of two spines on the coxal joint and one on 



Fig. 373.— Pleukoprkin intekmedii'm. x 10. 



