CETJSTACEA OF THE MEEGUI AECHIPELAGO. 149 



The Mergui Collection, wliicli 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 to a 

 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. 

 {Gnathograjpsus, A. M.-Edw.), and Pyxidognatlms, M.-Edw., and, 

 moreover, agrees in many other characters with the repre- 

 sentative of the latter genus. JPyxidognathus Deianira may? 

 however, be distinguished at first sight from PyxidognatTius 

 granulosus (and thus also from Sypsilograpsus 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 



* Coelochirus crinipes, Nauck, and Pachystomum 'philippinense, Nauck (1880), 

 are identical, the former with. Ptychognathus pilipes, A. M.-Edw., the latter 

 with Pseudograpsus alhiis, Stimps. (de Man, in Zoolog. Jahrbiicher, herausgeg. 

 Ton Prof. J. W Spengel, Jena, Bd. ii. p. 719, 1887). 



