PETALOPHTHALMUS PACIFICUS. 223 



comes necessary to modify Sans's diagnosis of the genus Petalophlhalmus * as 

 follows : — 



Sexes similar. Carapace short, leaving the last two thoracic segments 

 exposed. Eye-stalks leaf-like, without any visual elements or pigment. An- 

 tennular peduncle greatly elongated in both sexes, and without the usual 

 hirsute lobe in the male. Antennal flagellum small, antennal scale lanceo- 

 late or narrowly oval, setose on both margins. Mandibular palps prodigiously 

 developed in both sexes, forming powerful prehensile organs. Maxillipeds 

 devoid of exopods, but furnished with well developed epipods; nieral seg- 

 ment expanded interiorly so as to form a large linguiform lobe. Gnatho- 

 pods (or first pair of legs) short, strong, subcheliform, devoid of exopods ; 

 meral segment expanded on the inner side to form a very large, porrect 

 lobe. Terminal segment of fourth pair of legs (counting the gnathopods as 

 the first) obtuse and densely hirsute. Caudal limbs scarcely natatorj' even 

 in the male. Marsupial pouch of female comjiosed of seven pairs of incu- 

 batory lamellge, the anterior pair rudimentary. Apex of telson entire, not 

 incised in the middle. Outer plates of the uropods distinctly jointed near 

 the apex. 



In the " Challenger" specimen of P. armiger, the second and third pairs of 

 legs were imperfect, lacking all the joints of the endopods beyond the point 

 of articulation with the exopods. It is remarkable that these same joints are 

 lost from the same appendages both in the " Albatross" specimen of P-paci- 

 ficiis and in the P. anniger obtained during the cruise of the " Blake." 



Petalophtlialmus pacificus Fax. 



Plate LIV. 



Bull. Mus. Comp. Zobl., XXIV. 21S, 1893. 



Similar to P. anniger W.-Suhm, but different in some particulars. The 

 rostrum is more prominent, and thei'e is a median tooth on the carapace be- 

 hind the rostrum. The caudal limbs of the male are quite different from 

 those of P. armiger as described and figured by G. 0. Sars. In the latter 

 each pair of caudal limbs bears a slender cylindrical external branch, whilst 

 in P. pacificus the first pair is wholly destitute of an external branch, and the 

 second pair (Plate LIV., Fig. 1^) discloses but the slightest rudiment of such 

 a branch in the shape of a minute bud barely discernible with the aid of 



* Op. cit., p. 173. 



