THE POINT EXPLAINED 123 



CHAPTER rX 



TEIBE IV. OXYSTOMATA 



The carapace is convex or depressed, with the antero- 

 lateral margins arcuate or orbiculate ; or even subglobose ; 

 or more or less oblong, with subparallel or slightly con- 

 vergent margins (Dorippidse). The epistome is very much 

 reduced or rudimentary. The buccal frame is more or 

 less triangular, nearly always produced and narrowed 

 forwards with the margins anteriorly convergent. The 

 afferent channels to the branchiae open either behind the 

 pterygostoraian regions and in front of the chelipeds, or, 

 more rarely, at the antero-lateral angles of the palate 

 (Leucosiidffi). The efferent channels open at the middle 

 of the endostome which is produced forwards. There are 

 six to nine pairs of branchiae. The first antennee fold 

 longitudinally or obliquely. The third maxillipeds have 

 the fifth joint articulated at the inner or the outer front 

 angle or at the apex of the fourth, beneath which it is 

 often concealed. The verges of the male are exserted 

 either from the surface of the sternal plastron or more 

 usually from the bases of the fifth pair of legs, which are 

 either adapted for walking or for swimming, or are feeble 

 and raised upon the dorsal surface of the carapace. 



It is the nan-owing anteriorly of the buccal frame or 

 mouth-cavity ' that gives the name of ' sharp-mouths ' to 

 this tribe, which is divided into four families, the Calap- 

 pidas, Matutidae, Leucosiidee, and Dorippidse. 



Fwmily 1. — Oalappidce. 



The afferent channels to the branchias open behind 

 the pterygostoraian regions and in front of the chelipeds. 



