no. 2377. COPEPODS OF THE GENUS CLAUSIDIVM— WILSON. 427 



2 Posterior corners of cephalothorax, second, and third segments prolonged back- 

 wards outside each following segment; spines at the posterior corners of genital 

 segment. dissimile, new species. 



2. Posterior corners of cephalothorax, second, and third segments prolonged back- 



wards outside each following segment; no spines on genital segment; fifth leg 



with fine hairs between the setae vancouverense (Haddon), 1912. 



9. Posterior corners of cephalothorax, second, and third segments not prolonged; no 

 spines at posterior corners of genital segment; cephalothorax widest at poste- 

 rior margin apodiforme (Philippi), 1839. 



3. Cephalothorax twice as wide as long; dorsal plate of fourth segment covering the 



base of the fifth legs, not reaching the abdomen; anal laminae a half longer than 

 wide dissimile, new species. 



3. Cephalothorax a quarter wider than long; dorsal plate of fourth segment covering 

 the whole of the fifth legs and most of the abdomen; anal laminae three to four 

 times as long as wide apodiforme (Philippi), 1839. 



3. Cephalothorax a quarter wider than long; dorsal plate of fourth segment covering 

 the base of the fifth legs, not reaching the abdomen; anal laminae as wide as 

 long vancouverense (Haddon), 1912. 



3. First antennae half as long as the body, with short rigid hairs; abdomen and genital 



segment half the body length, but with only three segments in both 



caudatum (Say), 1818. 



CLAUSIDIUM DISSIMILE, new species. 



Host and record of specimens. — Twenty-five specimens, including 

 both sexes, were obtained by Prof. S. I. Kornhauser at Cold Spring 

 Harbor, Long Island, in the summer of 1915 from the gill chamber 

 of a species cf Callianassa dug up on the beach. Besides the adults 

 of both sexes there were also obtained many development stages. 

 A male and female, fastened together in the characteristic manner 

 already noted, and mounted in balsam, have been selected to serve 

 as types of the new species, and have been donated by Doctor Korn- 

 hauser to the National Museum, Cat. No. 54080, U.S.N.M. 



External specific characters of adult female. — First thorax segment 

 fused with the head to form a cephalothorax, which is twice as wide 

 as long and whose posterior corners are produced laterally and 

 backward. 



The antennal area is well marked, but there are no eyes, the places 

 mistaken for them by Kossmann being probably the points of at- 

 tachment of the second antennae. Second and third segments as 

 wide as the cephalothorax, but only a third as long, and also pro- 

 duced laterally and backward. Fourth and fifth segments fused 

 and covered with a single dorsal plate, which is twice as long as those 

 on the second and third segments, but only three-fourths as wide, 

 with rounded lateral angles and a strongly convex posterior margin. 

 This plate projects far enough laterally to cover the entire basal 

 joints of the fourth and fifth legs, but their rami project far beyond 

 its posterior margin. 



Through the center of the body the various dorsal plates are 

 thoroughly fused together, but their prolonged lateral margins are 



