574 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



latter condition the posterior margin of the trunk may be wholly with- 

 out processes ( TracJieUastes) or may have a single ventral pair (Para- 

 hracMella) or a single dorsal jniir (CJiaropinus) . 



In the third group we find genera in which there is no neck at all; 

 the head is short and wide and may be in line with the trunk axis or 

 inchned to it. Wlien the two are in the same line we may find a sin- 

 gle pair of processes on the posterior margin of the trunk which are 

 either ventral (Lernaeopoda) or dorsal (Lernaeopodina) to the egg 

 strings. If there are no posterior processes ( Vanhenedenia) the sec- 

 ond maxillae extend straiglit forward, are rigid, and their base has 

 been moved until they are virtually dorsal instead of ventral or 

 lateral, and cover the back of the head. Wlien the head and trunk 

 are inclined to each other we find no posterior processes, but there 

 may be an unpaired median genital process (Sahnincola) like that in 

 Clavella. The second maxillae are also usually turned backward along 

 the ventral surface of the trunk and their bases are connected around 

 the posterior end of the head by a stout ridge. 



Calling the second maxillae by the common name of arms, these 

 enlarged bases correspond to a pair of misshapen shoulders. 



Sometimes the trunk is covered with longitudinal rows of knobs or 

 tubercles (Basanistes) . Again there are neither knobs or shoulders, 

 but there is a w^eU-defined abdomen behind the bases of the egg 

 strings (AcJitheres) . 



General hody form of male. — The male never becomes fixed in posi- 

 tion and hence does not usually show as much degeneration as the 

 female. The second maxillae are never permanently attached by 

 means of a bulla and so do not develop into long arms, but retain 

 their claws and are very similar to the maxillipeds both in form and 

 function. The trunk is distinctly segmented more often than in the 

 female and is usually furnished at the posterior end with a pair of 

 weU-defined anal laminae. 



In some genera the cephalon and in others the whole body is cov- 

 ered with a carapace, but in the majority of genera this is lacking. 

 The male remains a pigmy and there is a greater disparity in size 

 between the two sexes than can be found anywhere else among the 

 parasitic copepods. 



There is also a folding of the body in these males, but in a manner 

 different from that just described for the females. 



In the female the cephalothorax was flexed either forward or back- 

 ward and sometimes rested against the dorsal surface of the trunk, 

 but there was no fusion of the two parts except in the single genus 

 Clavellisa. Here in the males, on the contrary, the cephalothorax is 

 always folded forward against the ventral surface of tlie trunk, and 

 the two are frequently so thoroughly fused as to be indistinguishable. 



