. Bulletin - United States National Museum. Science. 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
. Bulletin - United States National Museum. Science. 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, 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 pos
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