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



near the apex on the inner margin is a short and robust stylamblys, tipped with 

 eincinnuli. The outer branch is also short, rigid, and fringed with hairs that are 

 planted in lateral rows. The second pair of pleopoda (fig. lq) is subequal ; the outer 

 branch is long, ovate, foliaceous, and fringed with hairs, and the inner is nearly as 

 long but having the margin straight, and the basal portion supports a transversely 

 broad disc-like process that is matted with curved spines on the distal surface, from 

 the centre of which there springs a short but well-developed stylamblys tipped with 

 eincinnuli. The third pair of pleopoda is long, ovate, foliaceous, and fringed with hairs ; 

 on the distal margin of the inner branch there is a short stylamblys. The fourth and 

 fifth pairs resemble the third, but are a little shorter ; the stylamblydes in our specimen 

 have the eincinnuli on either side hooked together, thus holding the two appendages in 

 contact, and demonstrating their use. The sixth pair of pleopoda (PI. CXVIII. v, v) t 

 which helps to form the rhipidura, has the basal joint short, with two clefts, one upon the 

 outer side into which the outer ramus falls, the other on the upper surface in which the 

 inner ramus rests when the tail-fan is extended. The outer margin of the external 

 ramus is robust and rigid for a considerable distance, where it terminates in a small tooth 

 and an obliquely transverse row of regular bead-like points, marking the line of the 

 diseresis, which is separated or free for one-third of its extent. The distal extremity 

 of both the branches is rounded and broader than their base. On the posterior 

 ventral surface of the somite between the basal joints of the pleopoda there is a small 

 longitudinally compressed tooth, and on each side an elevated lunate process, separated 

 from the outer wall by a cleft and acting as a rest or support to the inward pressure of 

 the rhipidura. 



There are eight pairs of branchial plumes, six of which are pleurobranchial and two 

 podobranchial, as shown in the following table : — 



Pleurobranchia?, . . ....1 1 1 1 1 1 



Arthro branchiae, . . 



Podobranchia 1 , 

 Mastigobranchiae, 



Observations. — A. Milne-Edwards considers this species to be a variety of Atya 

 scabra, Leach, and says that "it appears to differ only in the feet, which are slightly 

 grooved, by the median piece of the tail (telson) presenting a more marked triangular 

 depression, and by the antennae not being more than half the length of the body." 



The original drawing, which is now in my possession, of Dr. Leach's figure in the 

 Zoological Miscellany, shows that in Atya scabra the second antennae are not so long as 

 the carapace, whereas in our specimen they reach to the sixth somite of the pleon, or 

 more than three-fourths the length of the animal, but I cannot discover any grooving 

 along the legs to correspond with Newport's description. 



