68 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



era], the body of the female is more compact than that of the male. 

 The thoracic segments tend to be more broadly joined to each other, 

 making the females less flexible and adapted for a more sedentary 

 existence. The male is not modified in this way and is more mobile 

 than the female (compare figs. 1 and 16). 



Cephalon: The cephalon is usually rounded in both sexes and 

 concave on the ventral surface. This configm'ation is quite stable 

 and found in most caligoid copepods. This is an obvious modifica- 

 tion to aid in attaching to the host, the cephalon forming a sucking 

 disc. The lateral borders usually bear a membrane. This thin 

 flexible membrane further enhances the holding ability of the cephalon. 



Thoracic segments: In all cases in both sexes segment 1 is fused to 

 the head and segments 2-4 are free. The thoracic segments of the 

 female may bear dorsal plates in one of two arrangements, plates 

 present on segments 2-4 as in Pandarus, Pseudopandarus , Gangliopus, 

 Phyllothereus, Perissopus, and Pannosus, or plates present on segment 

 4 only as in Echthrogaleus, Demoleus, Pagina, Dinemoum, Nesippus, 

 and Paranesippus. This feature separates the females easily into 

 2 distinct groups. 



Genital segment: The genital segment in both sexes is well formed. 

 In the female the genital segment may comprise more than one-half 

 of the total length (as in Pseudopandarus) and in all cases is at least 

 one-third of the total length of the copepod. 



Abdomen: The abdomen of the female is 1-segmented in all genera 

 except Pagina and Dinemoura. The segments of the abdomen bear 

 dorsal plates except in the genera Nesippus and Paranesippus. The 

 abdomen may be joined to the genital segment ventrally or terminally. 

 In the male the abdomen is of 2 segments except in the genus Nesippus, 

 in which there is only 1. None of the males have dorsal abdominal 

 plates. 



Caudal rami: There is a great deal of variation in the form of the 

 rami in the females of this family. In the genus Pandarus the rami 

 are attached laterally to the abdomen and are often strongly sclero- 

 tized and elongated, terminating in a point (see figs. 2, 28, 35, 110). 

 In Pandarus bicolor (see fig. 101) the rami are not elongated but are 

 attached laterally to the abdomen. 



It is interesting to note that the 2 genera Phyllothereus and Gang- 

 liopus, which are found only on gill filaments of the hosts, show a 

 great reduction in adhesion pads. Dinemoura ferox and D. discrepans 

 also have no adhesion pads. Both these species are found on the 

 body surface, and the loss of pads is unexplained in these cases. 



First antenna: In both sexes of all members of this family the 

 first antenna is 2-segmented. The first segment bears terminally 

 a number of spines that are often covered with spinules or hairs. 



