CRUSTACEA OF THE MERGUI ARCHIPELAGO. 163 
one, which is united with the chief portion at its base, so that 
each lobule is transversely sulcate near its posterior end. A 
similar structure is also found in J. distinctus, but in this 
species the lobules of the orbital portion, 12 or 13 in number, 
are much smaller, and decrease more gradually in size. The 
lobules of the postorbital portion decrease more regularly in 
size, and are rather granuliform. In the female the infraorbital 
ridge is not prolonged behind the orbits, so that a postorbital 
portion is wanting; the ridge is composed of 18-20 minute 
truncate teeth, the first ten or twelve of which are nearly equal, 
and the posterior ones only decrease slightly in size. 
This species, in the pterygostomian regions of its cephalo- 
thorax, and in the form and size of the male abdomen and of 
the outer foot-jaws, agrees with I. distinctus. The anterior 
margin of the buccal cavity also presents the same structure 
and form in both species. 
The chelipedes of the male differ from those of I. distinctus. 
In the adult specimen the left chelipede is much larger than the 
right, but in the younger specimens (the cephalothorax of which 
is less than 20 millim. broad) they are equal to one another. 
The arms do not project so far beyond the lateral margins of the 
cephalothorax as in IZ. distinctus ; when comparing specimens of 
both species with one another (the cephalothorax of which is 
17 millim. broad), the arms scarcely project beyond the lateral 
margins of the carapace in I. dentipes, whereas in I. distinctus 
they reach a little beyond even the middle of the meropodites of 
the third and fourth legs. In the adult specimen, however, the 
arms project nearly as far laterally as do those of the smaller 
M. distinctus. The arms have nearly the same form and struc- 
ture in both species, the upper surface being slightly enlarged 
towards the distal extremity; the “musical crest” lies on the 
middle third of the anterior margin, which is minutely denticu- 
lated at its distal half, like the posterior margin. In younger 
individuals the musical crest is found near the distal extremity, 
‘as in Helice tridens, de Haan. 
The wrist is somewhat granular above, especially on its pos- 
terior and anterior margins. The larger hand of the adult male 
is about twice and a half as long as it is broad at the base 
of the fingers. Though closely resembling MM. distinctus, the 
palm is, however, a little less elongate, its length being in pro- 
portion to its breadth (height) at the base of the fingers as 
1s 
