82 Mr. P. W. Bassett-Smith on 



small ; the hamulus is very small, slightly curved, and just 

 overlaps the border. 



Fourth perceopod very short, not reaching as far as the 

 border of the genital segment; it terminates in three short 

 simple hairs, with a fourth halfway down the lower border. 



Genital segment large, oblong, lobed posteriorly, slightly 

 narrower in front. 



Abdomen small, as broad as long, about one sixth the 

 length of the genital segment. Caudal plates longer than 

 broad, bearing three short terminal plumose setae and two 

 short hairs on the outer border. 



Egg- sacs long, as in Caligus. 



Length 5 millim. 



Caligus, Mull. 



Caligus aril, sp. n. (PI. IV. fig. 1.) 



This species was found in greater or smaller numbers on 

 every example of a " cat-fish " (Arius acutirostris) examined 

 at Trincomalee, Ceylon. During the month of October 1897 

 both sexes were present in various stages of maturity, and 

 appear never to attain any considerable size : during life 

 they were very active; the "lunula" were very marked, 

 projecting in front of the frontal border, the carapace markedly 

 vaulted, and colour quite transparent, without spots; the 

 posterior lobes of the genital segments in the immature females 

 were strongly marked. 



These animals were taken in company with Hermilius 

 longicornis and Lepeophtheirus longipalpus on the inside of 

 the operculum and on the roof of the mouth. This species 

 seems to be nearest allied to C. monacanthi, Kr., taken in 

 the "West Indies, differing, however, entirely in the details 

 of the swimming-feet, caudal plates, &c. 



In the female the cephalothorax was almost circular in 

 shape, slightly longer than broad, considerably shorter than 

 the remaining portion of the animal, narrowing rapidly ante- 

 riorly ; the posterior central lobe, which is broad, is separated 

 from the posterior lateral angles by a deep cleft, the whole 

 being strongly arched upwards and having the outer circular 

 edge bordered with a strip of very fine short parallel tubes. 

 Frontal plates of moderate size, somewhat indented in the 

 centre. Lunula? very large and prominent. 



Anterior antennce: first joint equal in length with breadth 

 of lunule, bearing about twenty small plumose hairs ; second 

 joint club-shaped, with fine terminal hairs. 



Posterior a)itenno3 placed well to the outer side of the 



