xo.uot. PARASITIC COPEPODS—CALIGID.E— WILSON. 635 



Such a marked restriction in the number of eggs would lead us to 

 search for some accompanying' advantages in the struggle for exist- 

 en >. One thing which suggests itself is a superior activity. All the 

 swimming legs in the adult are powerfully developed, particularly the 

 basal apron of the third pair. This constitutes the chief organ of 

 locomotion as already suggested, but whether there is a similar supe- 

 riority in all the stages of development only a careful study of the 

 nauplii and chalimus stage can determine. 



But the chief interest of the species lies in its morphological relation 

 to such forms as Caligus and Lepeophtheirus on the one side and the 

 genus Anuretes on the other. In the latter genus the anal laminae 

 are attached directly to the ventral surface of the genital segment, and 

 usually at some little distance from the posterior margin of the latter. 

 It would be difficult to know just how to account for the disappear- 

 ance of the abdomen were it not for the present species. But the 

 structure here seems to indicate clearly that, starting from the dorsal 

 surface and of a normal size, the abdomen has retreated gradually, 

 first to the ventral surface, and then away from the posterior margin, 

 diminishing in size all the while, until it has been finally absorbed 

 into the genital segment. 



The anal lamina? have not participated in the diminution, but, 

 retaining their original proportions, when the abdomen has disappeared 

 they still remain on either side of the anus as morphological indicators 

 of the degeneration which has taken place. 



LEPEOPHTHEIRUS PARVIVENTRIS, new species. 

 Plate XXIII, figs. 275-284. 



Female. — Carapace obovate, one-eighth longer than wide, broadest 

 posteriorly. Frontal plates of medium size and well defined; pos- 

 terior sinuses broad, shallow, and quite widely separated, leaving the 

 median lobe four-ninths of the entire width and rather squarely 

 truncated posteriorly. Lateral lobes broad and well rounded. Free 

 thoracic segment considerably less than half the width of the genital 

 segment, and of medium leugth. Genital segment a little more than 

 half the length of the carapace, as wide as long, and with nearly par- 

 allel sides and broad, well rounded posterior lobes. Abdomen quad- 

 rangular and very small, only one-third the length of the genital seg*- 

 ment, and wider than long. Anal laminae large and curved outward, 

 each one armed with four long plumose setae. 



The two joints of the first antenna? about the same length, and both 

 plentifully supplied with setae. The second antenna? short and small, 

 the terminal hook slender and strongly curved. 



The lirst maxillae are as huge as the claw of the second antenna? and 

 as strongly curved. The second maxillae are also large, the branches 

 slightly longer than the basal portion, and curved in toward each 



