372 BULLETIN 5', UNITED STATES NATIONAL MUSEUM. 



a peduncle of five articles and a flagellum of sixteen articles. The 

 basal article is short; the second and third are of equal length, and 

 longer than the first; the last two are one and a half times longer 

 than the third, and subequal. The flagellurn consists of sixteen arti- 

 cles. The raaxillipeds have a palp of five articles. 



The thoracic segments are all equal in length. The epimera of the 

 second, third, and fourth segments do not extend the entire length of 

 the lateral margins, but occupy more than three-fourths of the margin. 

 The anterior portion of the segment at the sides is excavate for the 

 epimeron, and the posterior portion projects laterally as far as the 

 exterior margin of the epimeron. The epimera of the last three 

 segments occupy the entire lateral margin, and are increasingly wider 

 posteriorly. All the epimera are large and conspicuous from a dorsal 

 view. 



The legs are similar in structure, and in the male are thickly fur- 

 nished with hairs on the free margins of the joints. Those of the 

 female have the propodus only furnished with thick bristles on the 

 inferior margin. 



The abdomen has two short segments, followed by one large ter- 

 minal segment, which has lateral rudiments of another partly coalesced 

 segment. The posterior portion of the segment is regularly and 

 broadly rounded, with a very small obtuse median point, rounded at 

 the apex. 



The upper division of the opercular valves is crossed obliquely by 

 a carina formed by the thickened anterior portion. 



The following observations and measurements were made by Dr. 

 James E. Benedict several years ago and intended for publication. 

 He has given me permission to publish them here. 



An examination of numerous lots from California to Alaska appear to show that 

 the sexual differences are more marked in this than is usual in species of the genus. 



Dana's figure is undoubtedly that of a male and agrees well with the specimens in 

 the collection. The legs of the male are densely covered with hair; their heads are 

 broad and very prominent. The outline of the thorax is but little arcuate. The 

 abdomen is broad and but little tapering. The heads of the females are much 

 smaller in proportion to the size and width of the animal than in the males. The 

 abdomens are more tapering and the third and fourth segments of the thorax are 

 wider, giving the animal a suboval outline. The terminal outlines of the abdomens 

 of both sexes are alike. 



In sorting the different lots preserved in alcohol the males can usually be separated 

 from the females by the color alone, the larger yellow specimens always proving to 

 be males, while the dark colored ones are usually, though not always, females, and 

 in this collection commonly with eggs. Some lots contain a large excess of one sex 

 or the other, while in other lots the sexes are associated in more even numbers. No 

 females were found with hair on the legs or a well-developed male without it. 



Doctor Stimpson says: "An exceedingly common species of a dark-green color 

 found among seaweeds on rocky or stony shores between high-water and half-tide 

 marks," 



