268 Messrs. J. Wood-Mason and A. Alcock on 
continued to the posterior margin of the carapace; its spines 
are larger, more compressed, and less inclined, though more 
eurved, than those cf the rostrum, and subequal, with one or 
two shorter and slenderer ones intercalated between them here 
and there. In addition to the dorsal ridge the carapace bears 
on each side four other longitudinal rows of spines: the first 
of these runs quite close and subparallel to the dorsal ridge 
from one end of the carapace to the other; the second com- 
mences with the antennulary spine, curves slightly down- 
wards and then slightly upwards to the cervical suture, 
whence it takes a straight course to the hinder margin, running 
parallel to the dorsal ridge; the third consists of the antennal 
spine and of two spines on the posterior half of the cephalic 
portion of the carapace ; the fourth, of five or six spines com- 
mencing with the branchiostegal spine, and runs along the 
middle of the prominent efferent branchial canal, and like the 
second has its spines connected by a ridge. 
The surface of the part of the branchiostegite coinciding 
with the subjacent branchial chamber is raised into a longi- 
tudinally oval convex-topped elevation, which is fringed at 
the edges with strong spines and bears an irregular row of 
five or six along its middle. Between the branchial eleva- 
tion and the almost horizontally inflected portion of the cara- 
pace are some smaller spines roughly in the same straight 
line with those on tbe efferent branchial canal. 
The abdomen is armed along the middorsal line with a 
spiniferous ridge similar to that of the cephalothorax and 
extending almost without interruption trom the base to the 
apex, beimg absent only in the basal half of the fifth tergum, 
on the sides of its terga and pleura with symmetrically 
arranged spines similar in form to those of the dorsal ridge, 
and on the edges of each of its pleura with several ex- 
ceedingly long and slender needle-like spines, besides smaller 
ones ; the number, form, arrangement, size, and direction of 
these spines, which vary within smal! limits in all of the 
above respects from specimen to specimen, will be best under- 
stood by reference to the accompanying figures. The first 
ebdominal somite is produced in front on each side at the 
junction of the tergum with the pleuron into a short, stout, 
bitid, and incurved process, which forms the abdominal ele- 
ment of the thoracico-abdominal hinge, and is received into 
the groove in the hinder margin of the side of the carapace 
already described. ‘Vhe pleura of the second abdominal 
somite are much more expanded in the female than in the 
male. ‘The telson is elongate-triangular or obclavate in out- 
line, its margin being at first rounded and then tapering in 
