ISOPODS FROM THE ALASKA SALMON INVESTIGATION. 



By HARRIET RICHARDSON, Ph. D. 

 ( bllaborator, Smithsonian Institution. 



The present paper is one of a series based on the collections of the Fisheries 

 steamer Albatross in Alaska, while engaged in the salmon investigation during the 

 summer of L903. Four new species of Isopoda are described herein, one of which 

 is the type of a new genus. A list of other Isopoda collected during the expedition 

 is given and Roci/iiela angustata Richardson is figured again. 



FLABELLIFERA OR CYMOTHOIDEA. 

 Family JBGIb\£. 



2Eg& symmetrica Richardson, new species. 



Body ovate, twice as long as broad. Color yellow, densely covered with light brown dots, which 

 form a regular line along the margin of each segment. Surface smooth. 



Head with frontal margin produced in a median point, which arches over the basal joints of the 

 antenna' and meets the frontal lamina or interantennal plate on the under side. The eyes are narrow 

 and elongate, composed of numerous ocelli. They are separated in front by a distance equal to the 

 length of une eye. The hist pair of antenna- extend to tin- posterior margin of the tirst thoracic 

 segment; the joints of the peduncle are not dilated, although the first two joints are somewhat wider 

 than the third, nor is there a process at the distal extremity of the second joint. The tirst two joints 

 are of equal length; the third is as long as the first two together; the flagellum is composed of eleven 

 joints. The second pair of antenna' reach the middle of the third thoracic segment; the flagellum is 

 composed of sixteen joints. The frontal lamina or interantennal plate is conical, with the distal end 

 flat, the proximal end produced to an acute point. 



The several segments of the thorax are about equal in length, the last one being slightly shorter. 

 The epimera are large, subquadrate, with the outer distal angle of the last, three produced posteriori) 

 beyond the margin of their respective segments. 



The first three pairs of legs have the propodus beset with three small spines along the inner margin; 

 the carpus is short and armed with one spine; the merns is provided with live spines, and the ischium 

 has one long spine at the outer distal angle. The following four pairs of legs are long and slender 

 furnished with hairs at the distal extremity of the joints and armed with a few spines. 



The tirst live segments of the abdomen are short; the first is the shortest and the fifth the longest 

 in the median dorsal line. The terminal or sixth segment of the abdomen is linguiform and rounded 

 posteriorly with serrulated margin. 



The uropoda extend a little beyond the posterior margin of the terminal abdominal segment; 

 the outer branch is narrow, ovate, ami pointed at the distal extremity; the inner branch is almost 

 twice as wide as the outer one; both have serrulated margins. 



L'll 



