502 PROCEEDINGS OF THE NATIONAL MUSEUM. voi,. xxxi. 



lateral angles of the second and third pleon segments are minutely 

 produced. 



The eyes are dark, irregular)}" rounded, the interval between them 

 less than the diameter of the eye and in large specimens reduced to 

 a very narrow space. The first antenna? do not reach the end of the 

 penultimate joint of the peduncle of the second pair. The}^ have a 

 five-jointed flagellum subequal in length to the peduncle, of which the 

 first and second joints are subequal, broader but not much longer than 

 the third. The second antennte are slender, with a fiagellum of about 

 twenty joints, nearly as long as the peduncle, in which the last joint is 

 considerably longer than the penultimate, more sointhemalethanin the 

 female. The mouth parts are on the whole all of the character usual 

 in the genus. In the first maxillse no palp could be detected, but in the 

 female a microscopic notch was seen in the position proper to the base 

 of the palp. 



Fui. 1. — Orchestia oostaricana, male. 



The first gnathopod of the male has a small pellucid prominence on 

 the fourth joint distally, and the inner margin of the fifth and sixth 

 joints boldly produced, the distal projection of the sixth much narrower 

 than that of the fifth, but extending beyond the little spinule-fringed 

 palm, which is matched by the small acute finger. In the female this 

 limb is dift'erently constructed, with a narrower second joint and no 

 pellucid ])ulbous prominences. As in the male, the fifth joint is con- 

 siderably longer than the sixth. The latter is narrow, fringed on both 

 margins with spines, and expands slightly to a small concave palm, 

 beyond which the small curved finger extends. 



The second gnathopod of the male has a long, slender second joint, 

 having on the proximal part of the front margin two little tubercles 

 near together, equal or very unequal. Tlie third joint is short, with a 

 distal projection in front, the fourth, joint of about the same length, 



