262 CRUSTACEA. 



The species here included, hitherto referred to Trapezia, have 

 many striking peculiarities, among which are, the claw of the tarsus, 

 the shorter arm, the hand bent downward at the extremity, 

 the posterior margins of the outer maxillipeds making a deep triangle 

 with one another, instead of a transverse line nearly, the less dis- 

 tance between the upper part of the second joint and the third joint 

 of the outer maxillipeds and seven segments to the male abdomen ; 

 besides, the anterior margin of the buccal area is not at all emargi- 

 nate for the termination of the efferent branchial canal, although a 

 slightly-raised longitudinal line will be observed upon the praelabial 

 surface. The character* of the front is also quite different in the 

 known species ; and the third joint or arm of the anterior legs, instead 

 of having an acute anterior apex, is rounded, and instead of being 

 dentate along the whole inner margin, is denticulate only at or near 

 the rounded apical margin. The sides of the carapax are usually 

 without a spine, though not uniformly so. The fingers of the larger 

 hand are in contact at apex, and the lower finger or thumb has a pro- 

 minent middle to the inner margin; in the smaller hand, they are 

 throughout in contact. 



The tarsus is pointed, as seen in a lateral view, and has a horny, 

 claw-like extremity, which same horny texture extends back either 

 side and also below, as shown on Plate 16. About the under sur- 

 face of the tarsus there are several spinules in pairs and transverse 

 series; and the claw portion is flattened below, with the margin a 

 little raised. 



The Trapezia digitalis, Edwards, Crust., i. 429, belongs to this 

 genus, and is distinguished, according to the description given, by 

 having the front armed with two small points at middle. 



Tetralia, DANA, Am. Jour. Sci. [2], xi. 224. 



1. Latera carapacis inermia. 



TETRALIA NIGRIFRONS. 



Frons subtiliter denticulatus, parce sinuosus, medio obsolete bi-lobatm. 

 Pedes antici valde incequi, carpo intus spini-acuto. Pedes 8 jjos/ic? 

 fere nudi, articulo tertio paris posterioris latissimo, sesqui longwre 

 quam lato, fere triplo latiore quam articulus quintus. 



