REPORT ON THE CRUSTACEA MACRURA. 47 



The first pair of antennae terminates in two long, slender subequal flagella. 



The second pair of antennae has a short and stiff scaphoeerite, and terminates in a 

 long slender rlaoellum. 



The siagon or mandible is strong, and carries a three-jointed synaphipod. 



The posterior siagnopod has the distal extremity of the outer branch formed into 

 an operculum, and the mastigobranchia is broad and well developed. 



The first pair of gnathopoda has neither branchial plume nor mastigobranchia, but ;i 

 rudimentary stump alone represents the latter. 



The second pair of gnathopoda supports a basecphysis, a well-formed podobranchial 

 plume and well-developed mastigobranchia. 



The three anterior pairs of pereiopoda are chelate, the first pair being much larger 

 than the others, the pollex and dactylos being longer than the propodos, although 

 unequal iu proportion on each side. The fourth pair is monodactyle, the dactylos short 

 and hairy. The fifth or posterior pair is minutely chelate, the dactylos being very 

 small and lost amongst a brush of hairs in the only specimen procured. But as this 

 description is taken from a female, it is not improbable that this may be a sexual rather 

 than a generic character. 



The form of the rhipidura, the length and increasing width of each posterior somite of 

 the pleon, and the form and character of the pereiopoda approximate the character of this 

 genus to Axius and others of the Thalassinidae. 



Thaumastockeles zaleuca (v. Willemoes-Suhm) (PL VI. b-q ; PI. VII. fig. 1, e-h). 



Adams zaleiicus, Willemoes-Suhm, Trans. Linn. Soc. Loncl., ser. 2, vol. i. p. 49, pi. x. fig. 1. 

 Thaumastocheles zaleuca, Wood-Mason, Proc. Asiat. Soc. Bengal, p. 181, 1874. 



Animal long and slender, sides subparallel and compressed, dorsal surface smooth 

 except on the antennal and post-ocular regions of the carapace, on each side of the 

 rostrum, and the third and fourth somites of the pleon, where there are numerous short, 

 thick tufts of hair. 



Rostrum dorsally flat. Ophthalmopoda absent. First pair of antennae subequally 

 biramose. Second about as long as the animal and carrying a strongly serrated scapho- 

 eerite, first pair of pereiopoda asymmetrical. The right being the larger and furnished 

 with a pollex and dactylos, nearly as long as the animal, slender and rod-like, curving 

 towards each other at the extremity, and armed on the inner surface from base to apex 

 with long spine-Hke teeth that interlock with each other when closed. 



Rhipidura having the outer plate large and strong and the inner small. Telson 

 quadrate. 



Length, 100 mm. (4 inches). 



Habitat— Station 23, off Sombrero Island, West Indies, March 15, 1873; lat. 

 18° 24' N., long. 63° 28' W.; depth, 450 fathoms; bottom, Pteropod ooze. 



