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



foliaceous plates, of which the inner is the larger, and exhibits a notch, from which 

 a bundle of long hairs projects, but no stylamblys is apparent. 



The sixth pair of pereiopoda forms part of the rhipidura or caudal fan. It articulates 

 with the posterior angle of the sixth somite ; the basal joint is short and broad, and 

 carries two sub-foliaceous plates ; the external is large, triangular, narrow at the base, 

 and broad at the extremity, the outer side is the longest, and projects forwards ; a 

 diasresis marks the external distal portion, but does not traverse the breadth of the plate, 

 which is strengthened in the middle by a longitudinal ridge ; the inner plate is much 

 smaller than the outer, and like it is traversed by a longitudinal ridge, and both are 

 fringed along the distal margins with closely-set hairs ; the external plate has a similar 

 row along the line of diaeresis. 



The specimen above described was taken in the dredge off Sombrero Island, in about 

 450 fathoms of water, on a bottom of Globigerina ooze. There is only one perfect 

 specimen in the collection, but fragments of a second, consisting of the gnathopod and 

 first pair of pereiopoda, appear to be parts of a more spinous variety, perhaps those of 

 a male form. 



The branchial arrangement of this species may be tabulated as — 



Pleurobranchiae, 

 Arthrobrancbiae, 

 Podobranchiae, . 

 Mastigobranchise, 



The branchial appendages are generally long. The podobranchiae are the longest, and 

 almost entirely cover and protect the arthrobranchiae and pleurobranchise, particularly 

 those of the four anterior pairs of pereiopoda. The mastigobranchiae form inter-branchial 

 plates similar to those of the Homarides ; they are long and broad, reach to the extreme 

 length of the branchial plumes, and are sparingly covered all over with long hairs that 

 spread out and penetrate between the branchial filaments. The hairs are generally 

 smooth and pointed. The inner surface of the carapace that covers the branchial chamber 

 is similarly beset with hairs of the same kind, this, with the mastigobranchial plates, and 

 pleura or floor of the branchial chamber, forms a division in which the several branchiae 

 of each appendage are shut off from the rest (PI. VII. fig. 1, \br) ; the pleurobranchia 

 lies beneath and rests upon the floor of the chamber, the arthrobranchise meet in the 

 centre, one on each side above the pleurobranchia, by a single row of short filaments that 

 nearly touch each other at their extremities ; the podobranchia covers and overlaps the 

 whole, while long, slender, and somewhat stiff hairs play between the several plumes of the 

 branchiae, as well as between the numerous filaments that compose them, and probably 

 keep the whole of the complex structure in constant motion. 



The posterior pair of periopoda possesses no podobranchia, arthrobranchia, nor 



