39 



339 



16; 1 c? 2?. West coast of Koh Kong, 10—15 fath.; I. 24; 1 c?. OfY Koh Kut, 6fath.; 

 I. 26 ; 2 c? 1 ?. 



In these specimens the ischium and merus of the outer maxillipeds are grooved 

 near the outer border, which is contrary to Alcock's description. I should be dis- 

 posed to consider the Siamese specimens a separate species, did not the shading 

 of the maxillipeds in Henderson's figure (pi. XXXVI, fig. 19, Trans. Linn. Soc. London, 

 Zool. (2), V, 1893) suggest a groove along the outer edge. In our specimens also, 

 the low branchial ridges are connected by a ridge across the cardiac region. In 

 this species the propodus of the first leg is distinctly longer than broad. 



Subfamily Asthenognathinæ. 

 Asthenognathus hexagonum Rathbun. 



Plate II, fig. 14. 

 Asthenognathus hexagonum Rathbun, Proc. Biol. .Soc. Washington, XXII, 111, 1909. 



Carapace I'/a times as wide as long, strongly hexagonal; the posterior margin 

 very little longer than the anterior, or fronto-orbital; antero-lateral and postero- 

 lateral margins subequal. Surface little convex, pubescent and finely punctate, 

 medial furrows deep. Front about ^/s as wide as carapace, advanced beyond the 

 orbits, sides oblique, lower edge straight. Orbits transverse, eyestalks tapering to 

 the black corneae. The granulate anterior and antero- 

 lateral margin is continued part way on the postero- 

 lateral margin. A small part of the carapace behind 

 the lateral angle is strongly deflexed, the true angle 

 being just above the base of the second leg. Posterior 

 margin strongly rimmed. 



The antennules are folded in deep fossettes. The 



infra-orbital ridge is strong and shaip. Buccal cavity 



arcuate in front, not nearly filled by the narrow outer 



maxillipeds. Ischium and merus of endognath subequal 



in length, ischium a little wider; segments of palpus 



end to end. Chelipeds of female feeble, little longer Fig. 2i. Astiienogathus hexagonum, 



than carapace, almost smooth, fingers longer than palm, 'J'P^ 9- ^'^ ■"'"• ^''J'^- "- anterior 

 J , , ... , , ,, ... border; b, chela: c, buccal cavity, 



acute, dactylus witli a sharp upper edge, pollex with 



a smooth ridge outside. Second leg longest, about twice as long as carapace, stout; 



third subequal to it; first much smaller; fourth most feeble, reaching little beyond 



merus of preceding pair. Male unknown. 



Length of ovigerous female 5-6 mm., width 78 mm., fronto-orbital width 43 

 mm., width of front along lower edge 17 mm. 



Type locality — North of Koh Kong, 8 fath., mud bottom; 1. 23; 2 c? (1 ovig., type). 



This species is very closely related to the type species, A. inœquipes Stimpson 

 (Smithson. Misc. Coll., XLIX, 140, pi. XIV, fig. 1, 1907). Chelipeds and legs similar 



