538 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 94 



leg at each posterior corner. Between this leg and the side of the 

 abdomen a flat rounded lamina is attached on each side to the posterior 

 margin of the genital segment on a level with its dorsal surface. The 

 abdomen is triangular, 1-segmented, with the apex posterior; the 

 caudal rami are curved, widely separated and nearly as long as the 

 abdomen, each armed with four setae of about the same size. 



The first antennae are 2-segmented and elongate, the segments of 

 equal length and armed with stout spines. The second antennae are 

 smaller than those of the female, the terminal claw strongly curved 

 and transversely wrinkled at its base but without any trace of teeth. 

 The mouth tube is short and pointed ; the inside mandibles are slender 

 and flattened, M'ith a row of 10 or 12 curved teeth along the inner 

 margin at the tip. The outside first maxillae are conical, each tipped 

 with a stout spine and having 2 small slender spines on the anterior 

 margin. The second maxilla has a slender and curved terminal seg- 

 ment one and a half times as long as the stout basal segment and bi- 

 partite at its tip. The maxilliped has a swollen basal segment and a 

 stout and slightly curved terminal claw. 



The first four pairs of legs are biramose, the rami of the first three 

 pairs 2-segmented, of the fourth pair 1-segmented, the setae distri- 

 buted as in figures 205 to 208. In the first and fourth pairs the exopod 

 is considerably longer than the endojDod, in the second and third pairs 

 the rami are about equal. Total length, 3 mm. Carapace, 2 mm. long, 

 1.86 mm. wide. 



Remarks. — ^Inasmuch as every one of the present males was at- 

 tached to a female in sexual union, it is absolutely certain that they 

 are the true males of the species and as such are the first to bei 

 described for the genus. In two other instances, however, other males 

 have unfortunately been ascribed by the present author to species 

 of this genus. The opportunity is taken liere to make the necessary 

 corrections : 



1. Wilson (1912, p. 235) : Two males of a lot of two males and 

 three females that were obtained from the pectoral fin of a sawfish 

 off the Cape of Good Hope. Since these five specimens were associ- 

 ated upon the same host with no other parasitic copepocls present, 

 the author assumed that they were the two sexes of the same species 

 and so described them under the name Achtheinus phiguis. The 

 three females were correctly diagnosed and they still remain the 

 types of the species pwgiu's, but a comparison of the males with those 

 here described discloses the fact that they do not belong to the genus 

 Achtheinus but that they must be referred to the genus Nesippvs. 



2. Wilson (1921, p. 6) : Two males of a lot of six females and 

 three males that were taken from the outside skin of Mustelus lunu- 

 latus off southern California. These were referred to the present 



