CRUSTACEA OF THE MERGUI ARCHIPELAGO. 159 
still smaller than the third. The lateral margins are fringed 
with short hairs, and the branchial regions of the upper sur- 
face are marked with three minutely granular lines, the anterior 
one of which is almost transverse, and terminates at the third 
antero-lateral tooth, whereas the other two proceed obliquely 
on the postero-lateral regions of the cephalothorax ; the latter 
are slightly pubescent. The upper surface of the carapace is 
a little convex, and the front is declivous and longitudinally 
grooved in the middle. The anterior margin of the front, which 
presents a small triangular incision in the middle, the breadth 
of which measures somewhat more than a fourth of the distance 
between the external orbital angles, makes very obtuse angles 
with the lateral margins of the front. 
The front is a little less prominent than the epistome, so 
that the latter is visible when the carapace is viewed from 
above. 
The infraorbital ridge was described by Milne-Edwards as 
“finement crénelé;” but these words are only exact when M. 
distinctus is compared with IZ. indicus. In M. indicus, M.-Edw., 
the infraorbital ridge is prolonged backwards to the level of 
the first antero-lateral incision, and only presents nine or ten 
teeth or lobules of very unequal size. The first four or five 
teeth are very small, and slightly increase in size; they are 
followed by two large rounded lobules. Behind the latter, and 
separated from them by a larger interval, three smaller, rounded, 
postorbital tubercles occur, constituting the postorbital portion 
of the ridge, and gradually decrease in size backwards. 
In Metaplax distinctus, on the contrary, the infraorbital ridge 
is continued backwards, behind the orbits, to the level of 
the second incision of the lateral margins of the carapace. In 
this species the ridge is composed of 25-30 small lobules, 
which successively, though slowly, decrease in size backwards. 
The first eight or ten lobules, which constitute the orbital 
portion of the ridge, are longer than broad, the following as long 
as broad, and the posterior fourteen or fifteen much smaller 
postorbital lobules are even a little broader than long. These 
small lobules are distinctly transversely sulcate on their upper 
margin. 
As in all species of Metaplax, the outer foot-jaws are widely 
gaping and provided with an oblique piliferous ridge; the 
merus-joint is nearly quadrate, being about as long ag broad, 
