342 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



pairs. The last article in all four pairs is very minute; the three pre- 

 ceding- articles are long and narrow. The last three pairs of legs are 

 ambulatory. 



Ortmann'^ says of this form: "Very j^oung- individuals are alwa^^s 

 without spines, and thus young- individuals always belong- to the var. 

 feUdeni {tuherosus)^ although their mother, to whose antenna3 they 

 cling, may be a true ha-ffrni. In larger individuals the spines are 

 developed in a different degree, and there are all intermediate stages 

 between the strongly spinous ^1. hajfjyii and the almost smooth A. 

 feildeni {ti(he7H>siis).^'' 



56. Genus PLEUROPRION zur Strassen. & 



Body with the fourth segment of the thorax not greatly longer than 

 the others. Marsupium as in the genus AretKrus. Abdomen com- 

 posed of only two segments, one segment anterior to the large ter- 

 minal segment. The head is united a least dorsally with the first 

 thoracic segment. The epimera are not distinct. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS PLEUROPRION. 



a. Head with three spines on the anterior part in front of the eyes. Third article of 

 the peduncle of the second antennae not longer than the second article and 

 armed with two sj^ines. Four spines present on posterior portion of head. 

 Two spines present, one on either side of the median line just below the con- 

 striction in the fourth thoracic segment. Two longitudinal rows of spines, one 

 on either side of the median line on the terminal abdominal segment. One 



spine present on basal joint of legs Plearoprion murdodd (Benedict) 



a^. Head with a single spine on the anterior part. Third article of peduncle of 

 second antennpe twice as long as the second article and unarmed. Two spines 

 present on posterior portion of head. Spines absent just below the constric- 

 tion in the fourth thoracic segment. Longitudinal rows of spines on last 

 abdominal segment absent. Two spines present on coxal joint of legs. 



PleuToprio)! hitcrmedmm (Richardson) 



PLEUROPRION MURDOCHI (Benedict). 



Arcturus rmirdochi Benedict, Proc. Biol. Soc. Washington, XII, 1898, pp. 49-50. — 

 Richardson, Proc. U. S. Nat. Mus., XXI, 1899, p. 855; Ann. Mag. Nat. 

 Hist. (7), IV, 1899, p. 277; American Naturalist, XXXIV, 1900, p. 230. 



Locality. — Point Franklin, Alaska. 



Body narrow, elongate, a little more than three times longer than 

 wide, 3i mm. : VI mm. 



Head wider than long, 1^ mm.: 3 nuu., with the front deeply exca- 

 vate between the lateral angles. The eyes are small, round, composite, 

 and situated at the sides of the head halfway between the antero-lateral 

 angles and the posterior margin. Just back of the anterior margin of 

 the head are three spines in a transverse row, one median and one on 



«Proc. Acad. Nat. Sciences, Phila., 1901, pp. 156-157. 



fcZool. Anzeiger, XXV, 1902, pp. 682-689; XXVI, 1903, p. 31. 



