ISOPODA. 105 



The lateral and posterior fins are composed of a peduncle and two 

 laminae, forming with the last segment a common fin shaped like a 

 fan. 



In these, the impressed and transverse lines of the anterior seg- 

 ment of the tail, which is always shorter than the next or last one, 

 do not extend to the lateral margin. The first joint of the superior 

 antennae has the form of a triangular palette. 



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

 leaflets of the fins are much flattened, and the intermediate piece or 

 the last segment is widened and rounded laterally. 



Zuzara, Leach. 



Leaflets of the fins very large; the superior, which is the shortest, 

 separates from the other to form a border to the last segment(l). 



Sphjeroma, Lat. 



Leaflets of a moderate size, equal, and laid one over the other(2). 



In those, the impressed lines or transverse sutures of the anterior 

 segment of the tail extend to its lateral edges and cut it. The first 

 joint of the superior antennae forms an elongated square, or linear 

 palette. 



The leaflets of the fins are usually narrower and thicker than in 

 the preceding ; the external sometimes (Cymodocea) incloses the 

 other, which is prismatic ; the point at which they unite resembles 

 a knot or joint. 



Sometimes the sixth segment of the body is visibly longer through- 

 out all its width than the preceding ones and that which follows. 



Only one of the two leaflets projects. 



Njesa, Campecopea, Leach(3). 



Sometimes the sixth segment of the body is as long as the preced- 

 ing ones and as that which follows. 



Cilicea, Leach. 



Only one of the fin-leaflets salient, the other being placed against 

 the posterior edge of the last segment(4). 



(1) Desmar., Consid., p. 298. 



(2) Desmar., Consid., p. 299302. Spherome derive, XLVII, 3;0niscus ser- 

 ratus, Fab. 



(3) Desmar., Consid., Nes4e bidentt, XLVII, 2;Campecopee velue, Id., It., 1. 



(4) Desmar., Consid., Cilicee de Latreille, XLVIII, 3. 



Vol. III. O 



