ORDER ISOPODA. 221 



In these the impressed lines, or transverse sutures of the 

 anterior segment of the tail, reach its lateral edges and divide 

 it. The first articulation of the upper antennae forms an 

 elongated palette, square or linear. 



The leaflets of the fins are usually narrower and more thick 

 than in the preceding. The exterior one sometimes emboxes 

 the other. The latter is prismatic. Their point of union 

 presents the appearance of a knot or articulation. 



Sometimes the sixth segment of the body is sensibly of 

 greater breadth than the ]jreceding and the following. One 

 of the two leaflets of the fins alone is projecting. 



N^s.^, Campecopea, Leach. 



Sometimes the sixth segment is of the length of the preced- 

 ing and the following. {Naesa bidentata, Desm.) 



CiLic^A, Leach, 



In which one of the leaflets of the fins alone is projecting, 

 the other being laid back against the posterior edge of the last 

 segment. {Ciliccsa, Latreillii, Desm.) 



Cymodocea, Leach, 



In which the two leaflets of the fins are projecting, and 

 equally directed backwards. The sixth segment is not pro- 

 longed posteriorly, and the last presents but a small lamina in 

 an emargination. 



Dynamene, Leach, 



Like cymodocea in the projection and direction of the leaflets 

 of the fins, but the sixth segment is prolonged behind, and 

 the last presents but a simple cleft, without lamina. 

 The others, such as 



