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



The body of the animal is covered over with a short, velvety pile, more scanty, 

 apparently from friction, upon the sides of the posterior somites of the pleon and the 

 lower part of the walls of the carapace. There is no crest on the dorsal surface of the 

 carapace posterior to the last tooth of the rostrum, which is armed with seven teeth in 

 the male and eight in the female that are equidistant, the last of the series terminating 

 in a line with the orbital margin of the carapace, and one tooth being separated from 

 the rest, standing on the gastric region. 



On the pleon the evidence of a dorsal carina commences on the second somite and 

 increases posteriorly on each successively until it forms a very distinct and perfect carina, 

 which terminates in a short tooth at the extremity of the sixth somite, and is indicated at 

 the posterior extremity of the two preceding somites. 



The ophthalmus is large, reniform, and stands on a short biarticulate peduncle. 



The first pair of antennae is longer than the rostrum, being subequal to the 

 length of the peduncle, and supports two short flagella which are not so long as the 

 last -two joints of the peduncle. The basal joint carries a prosartema that reaches to its 

 distal extremity, and a sharp-pointed stylocerite that extends beyond it. 



The second pair of antennas has the first three joints of the peduncle consolidated 

 into one, which articulates with the surface of the metope, and carries a scaphocerite, 

 and the terminal joint supports a flagellum that is twice as long as the animal. 



The mandible is a stout, short and powerful organ, and supports a quadrate, 

 biarticulate synaphipod, broader and shorter than that of Penasus canaliculatus, smooth 

 and evenly polished on the external surface, and projecting forwards, as a foliaceous plate, 

 to overlie the base of the second pair of antennas. The metastoma consists of two 

 oblong plates lying against the posterior surface of the mandible. 



The first pair of siagnopoda does not carry a long, slender, biarticulate outer ramus 

 as in Penasus canaliculatus. 



The second pair of siagnopoda corresponds closely with that of the preceding- 

 species, but has the posterior extremity of the mastigobranchial plate somewhat 

 broader. 



The third pair differs little from the typical form in the genus. 



The first pair of gnathopoda likewise differs little from the typical generic form. The 

 second pair carries a small, sharp tooth at the anterior extremity of the basis. 



The first pair of pereiopoda is armed with two teeth, one on the inner anterior 

 extremity of the ischium, and another in a similar position on the basis ; this latter joint 

 carries a short and slender basecphysis, and the coxa carries a short pedunculated 

 equi-biramose mastigobranchia. 



The second pair of pereiopoda is longer than the first, and is armed with one long and 

 slender tooth on the basis, which also supports a short and slender basecphysis, and the 

 coxa supports a pedunculated inequi-biramose mastigobranchia. 



