CRUSTACEA OF THE MERGUI ARCHIPELAGO. 149 
The Mergui Collection, which presents so large a number of 
interesting species, contains three specimens, namely, a probably 
adult female and two much younger males, which were collected 
in mangrove-swamps. These specimens apparently belong toa 
species hitherto unknown, which I refer to the genus Pyxido- 
gnathus *. 
This species presents the same remarkable and rare structure 
of the outer foot-jaws as the genera Ptychognathus, Stimps. 
(Gnathograpsus, A. M.-Edw.), and Pywidognathus, M.-Edw., and, 
moreover, agrees in many other characters with the repre- 
sentative of the latter genus. Py«idognathus Deianira may> 
however, be distinguished at first sight from Pysxidognathus 
granulosus (and thus also from Hypsilograpsus Deldeni) by the 
upper surface of the cephalothorax being smooth and glabrous, 
and presenting no other interregional grooves than the median 
transverse portion of the cervical suture. 
The cephalothorax is broader than long, the proportion of the 
breadth to the length being about as 4:3; P. granulosus also 
presents the same proportions. The cephalothorax is not extra- 
ordinarily thick. The carapace is nearly as broad anteriorly as 
posteriorly, and the lateral margins are scarcely arcuate; the 
upper surface is much convex anteriorly, declivous towards the 
lateral margins, and the front is strongly deflexed. The whole 
upper surface appears smooth to the naked eye; but when 
examined with a magnifying-glass, it shows everywhere minute 
punctations, a few larger being seen on the front and near 
the antero-lateral margins. It is only near the postero-lateral 
margins that the upper surface is slightly and minutely granular. 
The median part of the cervical suture and the branchio-cardiac 
grooves are very faintly indicated; all the other interregional 
grooves are completely wanting, and the upper surface appears 
smooth and convex. 
The front is considerably deflexed; and is situated between the 
internal orbital angles, which are as prominent as the front; the 
distance between the angles measuring about a third of the 
breadth of the cephalothorax. The front is separated, on each 
* Celochirus crinipes, Nauck, and Pachystomum philippinense, Nauck (1880), 
are identical, the former with Ptychognathus pilipes, A. M.-Edw., the latter 
with Pseudograpsus albus, Stimps. (de Man, in Zoolog. Jahrbiicher, herausgeg, 
yon Prof. J. W Spengel, Jena, Bd, ii. p. 719, 1887). 
