244 THE VOYAGE OF H.M.S. CHALLENGER. 



the median line posterior to the last tooth, and also channelled on each side, commencing 

 at the apex of the rostrum and terminating abruptly within the posterior margin of the 

 carapace. Pleon having the last three somites compressed and dorsally carinated, hut not 

 elevated to a tooth posteriorly. Telson acuminate and fringed with hairs at the sides. 

 Dorsal median line longitudinally channelled to the apex. 



Length, 76 mm. (3 in.) (male and female). 



Habitat. — Fiji Islands. 



Observations. — The specimens in the Challenger collection correspond in every detail 

 with that described by Milne-Edwards from the Mauritius, except that the largest 

 specimens of both males and females are only 76 mm. in length, whereas those taken 

 at the Mauritius, and with which we have compared our specimen, were 125 mm. 



Professor Milne-Edwards says that it is very like Penseus caramote, from which it 

 differs in having the dorsal crest less elevated towards the base of the rostrum, and in 

 having no tooth on the basis of the third pair of pereiopoda, and also in having none on 

 the lateral margins of the telson. It has been frequently described by various authors, 

 but I think that Stimpson 1 is justified in attaching "vix de-Haanii," to a specimen he 

 records from Loo Choo. 



This species differs from Penseus caramote in having the longitudinal ridges running 

 parallel from near the frontal margin to the posterior extremity of the dorsal carina, 

 whereas in Penseus caramote they are decidedly waved. Penseus caramote is also 

 described as having twelve teeth on the dorsal crest, whereas Penseus canaliculatus has 

 only nine, and the posterior is distant from the others and implanted over the gastric 

 region. In Penseus caramote the stylocerite reaches to the extremity of the eye, whereas 

 in Penseus canaliculatus it does not extend more than half the length. 



The ventral plate or thelycunr in the female also differs to a certain degree : in this 

 species it consists of two plates that meet in the central line at the posterior extremity, 

 and gradually opens anteriorly over a projecting floor, thus forming a cavity or hollow 

 space, whereas in Penseus caramote the two plates do not meet in the central line. There 

 is also a tooth on the basisal joint of the third pair of pereiopoda in Penseus caramote, 

 but none in the same position in Penseus canaliculatus. Penseus caramote has, more- 

 over, two teeth on each side of the telson, whereas in Penseus canaliculatus there is none. 



The coxes of the pereiopoda on each side are not very distinct, and the fifth pair 

 is furnished with a foramen for the passage of the vas deferens. The anterior pair of 

 pleopoda is single-branched ; attached to the basisal joint is a pair of membranous plates 

 or curtain-like organs, the petasma, which are connected in the median line by a series of 

 small hooks or cincinnuli (PI. XXXII. fig. 1" $ ). These two foliaceous plates are folded 



1 Prodronius description, anim. everteb., Proc. Acud. Nat. Sci. Philad., 1866, p. 113. 



2 From Hyhvxov, peculiar to the female. 



