CRUSTACEA OF THE MERGUI ARCHIPELAGO. 123 
_ the shape of its carapace, which is remarkably narrowed ante- 
riorly. Nearly the whole upper surface of the cephalothorax is 
covered with minute granules, but the mesogastric lobe is smooth 
and frequently the middle‘of the anterior cardiac region. The 
branchial regions present two somewhat oblique and parallel 
granular ridges, and the margins also of the cephalothorax appear 
granular. The lateral margins diverge considerably backwards in 
this species, and present three incisions, the anterior being the 
most. distinct ; the second is found nearly in the middle, or 
a little before the middle, of the lateral margin, and the third 
incision is so very indistinct, that it may easily be overlooked. 
A short transverse granular ridge is also found above the in- 
sertion of each of the two posterior legs, close and parallel to 
the posterior margin of the carapace. 
The chelipedes of the adult specimens are nearly equal to one 
another. The upper margin of the arm is somewhat granular, 
also the external margin; both the upper and the anterior 
margins of the arm are clothed with rather long hairs. The 
inner surface of the arm is armed with a short, horny, longi- 
tudinal crest, situated close to and a little beyond the middle of 
the anterior margin and parallel to it. This crest, which was 
not described by Messrs. Eydoux and Souleyet, is doubtless 
homologous with the ‘‘ musical crest’ of the genera Metaplax 
and Helice, described further on. The chelipedes of the female, 
as is usual, are much smaller than those of the male, and the 
inner surface of the arm is not provided with the horny musical 
crest characteristic of the latter sex. 
In the male, the upper surface of the wrist and the outer 
surfaces of the hands and fingers are quite smooth; the upper 
margin of the palm, however, is a little granular at its proxi- 
mal end. Both fingers have somewhat excavated, spoon- 
like tips; the inner margin of the immobile finger is armed with 
a strong, minutely denticulated tooth a little before its middle, 
and with a dozen very small teeth between the large tooth and 
the tip. The mobile finger is minutely granular on its upper 
margin, when examined under a lens; and its inner margin ~ 
presents a small, somewhat quadrangular tooth at the base, and 
fourteen or fifteen very small teeth between the quadrangular 
tooth and the tip, similar to those of the index. The inner 
surface of the palm is unarmed, smooth, and covered with a close 
down of hairs; in many specimens, however, and perhaps always’ 
