332 AMrniroDA normalia. 



carpus with the inferior angle rounded ohliquely and furnished 

 with a singk' liair ; propodos one-fuurth the breadth of the carpus, 

 incre;ising in width anteriorly, cxhil>iting a decided anterior mar- 

 gin or palm ; dactylos long, sharp, slightly curved, but not capable 

 of reaching the carpus : second pair uniform with the fii-st. First 

 pair of pereiopoda having the meros not longer than the ischium, 

 and furnished with a solitary hair at the infero-chstal extremity ; 

 carjius not longer or broader than the meros, having the infero- 

 distal margin oblique and fm-nished with a solitarj' hair ; propodos 

 longer and narrower than the carpus, and having the infero-distal 

 extremity furnished with a solitary hair that is half the length of 

 the dactylos ; dactylos nearly as long as the propodos, slender and 

 tapering. Second pair uniform with the first. Third pair* of 

 pereiopoda having the bases distally dilated, but not broader than 

 half its length ; ischium and meros subequal in breadth and length, 

 the latter furnished with a soUtaiy hair ; carpus tapering, the in- 

 ferior angle very oblique and defined hj a solitary hair ; propodos 

 narrow, straight, margins parallel, furnished with a sohtary hau* 

 at the inferior distal extremity ; dactylos sharp, slightly curved, 

 nearly as long as the propodos. Foiu'th pair uniform with the 

 tliird. Fifth pair as long as the preceding, having the bases not 

 dilated ; the three succeeding joints subequal, the carpus alone 

 being furnished at the inferior angle with, a short solitary hair ; 

 propodos longer and narrower than the carpus ; dactylos obsolete. 

 Thi'ee posterior paii's of pleopoda double-branched ; rami imequal, 

 long, narrow, straight, sharp, styliform. Telson rounded. 

 Length ^th of an inch. 



3. DITHYRUS. 



Dithyrus, Dana, U. S. IJxplor. Exped. p. 1009. 



'' Pleon closing well on the inferior siu-face of the pereion. Cephulon 

 transvei'sely ovate. [Ophthalmic] j)igments not large. Inferior 

 antennte concealed beneath the sides of the cephalon, not folded. 

 Three posterior pairs of pereiopoda reduced to mere basa, which are 

 veiy broad and clypeate. Gnathopoda [complexly] subcheliform. 

 Pleon five-jointed. Telson triangular."' — Dana. 



This genus appears to differ from Platyscelus only in having the 

 pereiopoda not developed beyond the basa. 



1. Dith3mis Faba. (Plate LIU. fig. 1.) 



Dithyrus Faba, Dana, TJ. S. Explor. Exped. p. 1010. pi. 69. f. 3. 



" Cephalon transverse, tumid, rounded in front. [Ophthalmic] pig- 



