CRUSTACEA OF THE MERGUI ARCHIPELAGO. 165 
resemble each other, and have on the lateral margins three or 
four incisions, which cause them to appear four- or five-toothed. 
In I. distinctus the first two antero-lateral teeth are almost equal 
to one another, the first tooth (the external orbital angle) 
being scarcely larger than the second; in IW. elegans, however, 
the second tooth is distinctly larger than the first. In both 
species the front is less prominent than the anterior margin 
of the buccal cavity ; but the median lobe of the anterior margin 
of the buccal cavity is more prominent in M. elegans. 
The infraorbital ridge is very finely crenulate in the male, 
even more delicately than in JL distinctus, and, as in that 
species, the ridge is continued backwards nearly opposite to 
the second antero-lateral incision. In Jd. distinctus the 
ridge is composed of 25-30 small lobules, of which the first 
eight or ten, constituting the orbital portion, are longer than 
broad, and transversely sulcate above. In JL. elegans, on the 
contrary, the ridge consists in the male of 50-60 minute rounded 
teeth or granules, which gradually and regularly decrease in 
size backwards; in the female, the ridge, as usual, is not pro- 
longed backwards behind the orbits, and consists of 35 teeth, which 
are similar to those of the male. 
As regards the pterygostomian regions and the shape and 
structure of the outer foot-jaws, both species completely agree 
with one another, but the abdomen of the male is a little differ- 
ent. In MW. elegans the first (or terminal) joint is triangular, 
rounded, and shorter than broad at the base; the second joint 
is longer than the first, and broader than long, the proportion of 
the breadth of its posterior margin to its length being as 32 : 2. 
- The third joint is much shorter than the second. 
The chelipedes of the male of JZ. elegans are nearly the same 
size as those of AZ. distinctus, and their arms project as far 
beyond the lateral margins of the carapace. The anterior legs 
are, however, more or less unequal, the right or the left being 
the larger; the arms are somewhat thickened in the middle, 
and again narrowed at the distal extremity, that part of the 
anterior margin of the upper surface which bears the musical 
crest projecting a little more forward than in JZ. distinctus. 
The hands of the adult male much resemble those of the latter 
species, the palm being longer than broad (high); but they are 
a little less slender, the proportion of the length of the palm (of 
the larger hand) to its breadth (height) at the distal end being 
