BRITISH COPEPODA. 



Sub-Class-ENTOMOSTRACA, Muller. 



(Gnathopoda, H. Woodward.) 



Order— COPEPODA. 



Section I. — Gnathostoma, Thorell. 



Family 1. Calanjm, Dana. 



Body elongated ; composed of from ten to twelve 

 segments. Abdomen nearly cylindrical, much nar- 

 rower than the cephalothorax and prolonged at the 

 posterior extremity into two more or less cylindrical 

 caudal branches. First segment of thorax often 

 anchylosed with the head ; fourth and fifth segments 

 also often coalescent. Head only rarely divided 

 into two segments. Anterior antennas very long 

 and composed of twenty-four or twenty-five joints ; 

 that of the right side in the male often modified for 

 grasping. Posterior antennas large, composed of a 

 basal joint from which spring usually two branches, 

 the primary branch consisting of two, the secondary 



