700 THE VOYAGE OF H.M.S. CHALLENGES. 



The ophthalmopoda are somewhat larger than in Atya bisidcata, reaching nearly to 

 the extremity of the rostrum, and have the ophthalmus not broader than the peduncle. 



The first pair of antennae has the first joint of the peduncle subequal with the rostrum 

 and the distal margin fringed with small, equal comb-like spinules ; the stylocerite on 

 the outer margin is equal in length with the rostrum and subequal with that of the first 

 joint of the antenna. The second and third joints resemble those of Atya bisidcata, 

 and the under surface of the third is anteriorly fringed with hairs, but not so densely 

 as in the former species. The flagella in the type are broken, but a comparison with 

 another specimen makes it probable that they are a little shorter than those of 

 Atya bisidcata. 



The second pair of antennae is about half the length of the animal, and nearly 

 corresponds in form with that of Atya bisidcata. The scaphocerite exhibits a corre- 

 sponding diaeresis, originating at the outer margin in front of the external tooth, and 

 passing transversely across the squamous portion in a curved direction. 



I have not disturbed the oral appendages in this species since there are only two 

 specimens, but I assume that they differ in as small a degree from those of the typical 

 species as do the other parts which have been fully examined. 



The first two pairs of pereiopoda appear to correspond specifically with those of 

 Atya bisidcata. The third pair seems to differ by the presence of a small tooth on 

 the under and outer side of the meros, and another at the anterior and lower angle of the 

 carpos, and the unguis of the dactylos is a more decided feature. 



The fourth and fifth pairs of pereiopoda, so far as preserved, resemble the third, but 

 are slightly more slender and the armature is more feeble. 1 



The first and succeeding pairs of pleopoda offer no distinctive feature, so far as can 

 be determined without dismemberment, from those of other species, and the telson and 

 lateral plates of the rhipidura likewise correspond. 



Atya bisidcata (Randall) (PI. CXX.). 



Atyoida bisidcata, Randal], Journ. Acad. Nat. Sci. Philad., vol. viii. p. 140, pi. v. fig. 5. 

 ,, „ Dana, U.S. Explor. Exped., Crust., p. 540, pi. xxxiv. fig. 1. 



,, „ Stiinpson, Proc. Acad. Nat. Sci. Philad., January 1860, p. 97. 



The dorsal surface of the carapace is smooth and not carinated until near the 

 rostrum, which is elevated in the median line and produced anteriorly to beyond the 

 extremity of the first joint of the first pair of antennae ; it is a little longer in the 

 male than in the female. On each side of the central carina there is a small channel 

 that dies out just behind the orbital margin. The anterior margin of the carapace is 



1 The three posterior pairs of pereiopoda are more robust than they are represented in the figure of the whole 

 animal (fig. 2), and correspond more nearly with the detached figure (tig. 2m) on the same Plate. 



