REPORT ON THE COPEPODA. 73 



This genus, in the structure of its mouth apparatus, especially of the foot-jaws, shows a 

 close relationship with Pontella, but the imperfect geniculation and absence of serrated 

 plates in the anterior antennae of the male, the peculiarly nodose and laxly setiferous 

 character of those organs, the rudimentary form of the fifth pair of feet (especially in 

 the female), and the small secondary branch of the posterior antenna, together with various 

 minor differences in the spinous armature of the swimming feet, amply distinguish it from 

 that genus. 



. From Corynura, a still more closely related genus, it is separated by the absence of 

 serrated antennal plates, and by the structure of the maxillae and tail. 



All the members of the genus are usually colourless and almost transparent ; and though 

 not occurring so abundantly as many other Copepoda, are very widely distributed in all 

 the great oceanic areas. 



1. Acartia laxa, Dana (PL XXXII. figs. 1-1 1). 



Acartia laxa, Dana, Crust. TJ. S. Expl. Exped., p. 1123, pi. lxxix. fig. 5, a-c. 



Length, 1-1 8th of an inch (T4 mm.). Female. — Cephalothorax (fig. 1) elongated, 

 very slightly tapered towards each extremity, obtusely pointed in front, truncated behind, 

 posterior lateral angles produced into sharp, slender spines. Anterior antennae (fig. 2) as 

 long as the body, of nearly equal thickness throughout, bearing a few very long setae, 

 which are distributed somewhat as follows : — three or four near the base, on the third, 

 fourth, and fifth joints ; two or three in the middle, on the tenth and eleventh joints, and 

 ten on the last five joints. The fifth pair of feet small (fig. 10), their two setae about equal 

 in length. The first segment of the abdomen (fig. 1 1) is equal in length to the remaining 

 four, tumid, and armed with a slender spine on the posterior dorsal angle ; the second 

 segment is much produced downwards and backwards ; caudal segments short, about as 

 broad as long ; setae equal, spreading widely in a fan-shaped manner, and about as long 

 as the abdomen. 



Habitat. — Philippine Islands ; between Arrou and Banda ; Atlantic Ocean at several 

 points between lat. 12° 16' S., and lat. 10° 55' N. 



The presence of spines on the posterior lateral angles of the cephalothorax is the most 

 tangible distinction between this and the following species ; there is also a slight difference 

 in the structure of the fifth pair of feet in the female (those of the male have not been seen), 

 and in the anterior antennae, which in Acartia laxa show no toothed marginal processes. 



2. Acartia denticornis, n. sp. (PL XXXI. fig. 1, and PL XXXII. figs. 12-17). 



(!) Acartia limpicla, Dana, Crust. U. ? S. Expl. Exped., p. 1119, pi. lxxix. fig. 2, a.b. 

 Length, l-22nd of an inch (1*1 mm.). In general shape similar to Acartia laxa, 

 except that the posterior angles of the cephalothorax are rounded off, and destitute of 



(ZOOL. CHALL. EXP. PART XXIII. 1883.) Z 10 



