Indian Deep-sea Dredging. 267 
a distinct marginal raised rim extends from the subbranchio- 
stegal spines backwards on each side, increasing towards the 
posterior margin, being especially well-marked posterolate- 
rally, where it rises into a strong and bold ridge, forming at 
each end of the carapace the posterior boundary of a deep 
groove; the ridge with the groove concentric therewith con- 
stituting the thoracic element of a strong thoracico-abdominal 
hinge. 
The branchiostegites are abruptly inflected, and their free 
margins, which are closely applied to the bases of the legs, 
are widely but obtusely angulated inwards opposite to the 
interval between the first and second pairs of legs anteriorly, 
while posteriorly they give off a triangular process which 
abuts against the posterolateral face of the eighth thoracic 
sternum, and thus serves not only to keep the tio elements | 
of the thoracico-abdominal hinge in constant relation of appo- 
sition with one another, but also to divide that which answers 
to the afferent branchial cleft in Astacus into two parts, an 
inferior and a superior: in the former of these the free margin 
of the carapace is in such close contact with the leg-bases as 
to leave no passage for water to enter; the latter, on the 
contrary, is a wide and rigidly-patent oval aperture placing 
the branchial chamber of its own side in direct communication 
with the subabdominal cavity, and forms the exclusive inlet 
for the water required for respiration : whence it follows that 
all the water which enters the branchial chambers must do so 
by way of the subabdominal cavity, and that during lite a 
constant circulation must be maintained in this cavity; in 
the female, in which the special afferent branchial apertures 
are larger than in the male and the subabdominal cavity 
forms a spacious brood-pouch, the constant circulation of 
water in the latter must secure a more perfect aeration of the 
egos than would otherwise occur; there is no doubt, in tact, 
that we have here to do with a mechanism for securing the 
due aeration of the eggs similar to that which exists in 
Encephaloides Armstrong and other deep-water Brachyura 
(Ann. & Mag. Nat. Hist. (6), vil. pp. 259, 266, et 267), 
wherein the branchial cavities communicate with the brood- 
cavity by means of canals in the hinder angles of the cephalo- 
thorax and, the ordinary direct channels being closed, water 
for respiration is derived from the brood-cavity. 
The rostrum is compressed, and presents four longitudinal 
spiny ridges—one dorsal, two lateral, and one ventral; the 
spines of these are all sharp, slender, forwardly curved and 
inclined, and decrease in length from the base towards the 
obsoletely bifid apex of the rostrum. The dorsal ridge is 
20% 
