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



Station 196, October 13, 1874 ; lat. 0° 48' 30" S., long. 126° 58' 30" E. ; near 

 the Philippines ; depth, 825 fathoms ; bottom, hard ground ; bottom temperature, 36° - 9. 

 Three specimens ; one female and two males, one of the latter not fully developed. 

 Trawled. 



This species appears to be readily detected by its colour. All the others are pale and 

 transparent, while the specimens of this species are all of a ferruginous red, although 

 they were taken at two stations separated by five degrees of latitude and eight of 

 longitude from each other. They all lived at nearly the same depth, and under nearly 

 the same temperature. Besides the variation in the ventral aspect of the two species, 

 the form of the mastigobranchial plates corresponds more closely with those of Haliporus 

 obliquirostris than with those of Haliporus equalis. 



It may be that the three forms are only varieties adapted to variable conditions 

 of habitat ; but resting upon the extent of our present knowledge of species, I consider 

 myself justified in separating them from each other, if only to demonstrate that variable 

 parts may under different conditions become permanent or specific characters. 



Sicyonia, Milne-Edwards. 



Sicyonia, Milne-Edwards, Ann. d. Sci. Nat., ser. 1, torn. xix. p. 339, 1830; Hist. Nat. Crust., 

 t. ii. p. 408. 



Dermal structure extremely hard and rigid. Laterally compressed ; anterior portion 

 of the carapace and posterior portion of the pleon more compressed than the central 

 region. Carapace furnished with a short rostrum, generally denticulated on the upper 

 surface. 



The ophthalmopod is short. Ophthalmus reniform. 



The first pair of antennae carries a sharp stylocerite and a rudimentary prosartema, 

 and terminates in two subequally short flagella. 



The second pair of antennae supports a scaphocerite that is broad at the base, narrow 

 at the apex, strong and rigid on the outer side, and terminates in a strong sharp tooth, 

 and the peduncle carries a moderately long flagellum. 



The oral appendages resemble those of Penseus generally, but differ in some details, 

 as may be seen in the description of Sicyonia carinata, which I have taken as being 

 typical of the genus. 



The first pair of gnathopoda carries a mastigobranchial plate without a podobranchia 

 attached to it, one arthrobranchial and one pleurobranchial plume, but no basecphysis. 



The second pair of gnathopoda has a long and slender mastigobranchia, one arthro- 

 branchial and one pleurobranchial plume, but no basecphysis. 



The anterior three pairs of pereiopoda are short, chelate, and carry a long and slender 



