74 

 PiLUMNOPLAX, Stimpson. 



Pdumiioplax, Stimpeon, Proo. Aoad. Nat. Sci. Philad. 1858 (1859) p. 93 : Miere, Challenger Brachyura, p. 225. 



Closely related to Carcinoplax from which it appears to differ only in the 

 following particulars : — 



(1) The carapace, instead of being convex fore and aft, is fiat and de- 

 pressed. 



(2) The front is somewhat broader and the orbits are deeper. 



(3) The ridges that define the efferent branchial channels are rather less 

 distinct. 



Pilum,nOJ)lax Sinclairi, Alcock and Anderson. Plate III. fig. 1. 



Carapace subquadrilateral, much depressed, a little more than three-quarters 

 as broad as long, very finely frosted, perfected bare, the regions fairly indicated. 



Front horizontal, slightly prominent, square cut, grooved but not distinctly 

 notched in the middle, more than a third the greatest breadth of the carapace ; 

 its free edge is turned vertically downwards to form a narrow concave facet with 

 raised margins. 



The antero-lateral borders are not much more than half the length of the 

 postero-lateral : they are thin and sharp, and are cut into three teeth, of which 

 the first is broad and somewhat emarginate and the other two are acute. On the 

 postero-lateral borders, just behind the junction with the antero-lateral, is a 

 denticle. 



The eyes are small but well-formed, and are freely movable. The orbits 

 conceal the retracted eyes to dorsal view : their upper margin is fissured near 

 the middle, and the lower margin is slightly excavated just below the outer 

 angle : the inner angle of the lower margin is not prominent, though dentiform. 



The antennules fold transversely, and their fossge are freely open to their 

 respective orbits. 



The basal antenna-joint is short and slender : the next joint reaches the 

 front : the flagellum, which arises in the orbital hiatus is about twice the length 

 of the orbit. 



The outer maxillipeds completely close the buccal cavern. 



The chelipeds in the female (male unknown) are unequal, the larger one 

 being not quite twice as long as the carapace : their surface, under the lens, is 

 finely frosted : the inner angle of the wrist is strongly pronounced and is capped 

 by a pair of acute teeth. 



Legs moderately stout, unarmed, smooth, almost hairless : the third pair, 

 which are somewhat the longest, are about two-and-a-half-times the length oi' 

 the carapace. The dactyli are compressed-sty liform. 



