220 CLASS CRUSTACEA. 



sents but two complete and mobile segments, but has 

 often on the first some impressed and transverse lines, indi- 

 cating the vestiges of other segments. On each side of its 

 posterior extremity is a fin terminated by two leaflets, the in- 

 ferior of which alone is mobile, and the superior is formed by 

 an internal prolongation of the common support. The bran- 

 chial appendages are curved interiorly. The internal side of 

 the first is accompanied in the males by a small linear and 

 elongated piece. The anterior part of the head, situated 

 under the antennae, is triangular, or in the form of an inverted 

 heart. 



Some have the body oval or oblong, in a state of contrac- 

 tion assuming the form of a bell. The antennse are termi- 

 nated by a pluri-articulate articulation, and the inferior at 

 least sensibly longer than the head. The lateral and poste- 

 rior fins are formed of a peduncle and two lamina, composing 

 with the last segment a common fan-like fin. 



In these the impressed and transverse lines of the anterior 

 segment of the tail, always shorter than the following or the 

 last, do not reach the lateral edges. The first articulation of 

 the upper antennae is in the form of a triangular palette. 



The head, seen from above, forms a transverse square. 

 The leaflets of the fins are very much flatted, and tlie inter- 

 mediate piece, or last segment, is widened, and rounded late- 

 rally. 



ZuzARA, Leach, 



In which the leaflets of the fins are very large, and the upper, 

 being shorter, is removed from the other to form a border to 

 the last segment. 



Sph^roma, Latr., 



In which the leaflets are of middle size, equal, and applied 

 one upon the other. Sph. dentata, Desmarest. 



