28 CARCINOLOGICAL STUDIES. 



11. Gelasimus arcuatus de Haan. 

 (PI. 3, fig. 7). 



Gelasimus arcuatus^ de Haan, Fauna Japonica, Crustacea, p. 53, 

 PI. VII, fig. 2. 



This Japanese species is apparently still insufficiently 

 known. I have before me two typical specimens from the 

 Leyden Museum, one of which agrees exactly with the 

 quoted figure in de Haan's classical work, whereas the 

 other represents an interesting individual variety. 



It differs from Gelas. vocans M. E. and Gelas. tetragonon 

 Herbst by the form of the cephalothorax , which is strongly 

 convex in the antero-posterior direction, and considera- 

 bly narrowed backwards; its lateral margins , defined 

 by a rather prominent carina which is only slightly granu- 

 lated anteriorly, present a characteristical S-like 

 course, which has been very well figured by de Haan. 

 The orbits are transverse, so that the acute external 

 orbital angles , which are directed almost straightly forward 

 and scarcely outward, project nearly as far forward as the 

 middle portion of the upper orbital margin. The inferior 

 one of the two lines which form the upper orbital margin 

 is distinct and tolerably far distant from the upper line. 

 The inferior margin presents no trace of an accessory row 

 of granules; this margin is distinctly crenulate along its 

 whole length. The frontal furrow is narrow and linear 

 with parallel margins, but its form appears rather 

 triangular in the figure of de Haan , which is not exact. 



The anterior margin of the arm of the larger chelipede 

 of the male is n ever armed with a prominent tooth, 

 which exists in Gelas. vocans and in Gelas. tetragonon , but 

 it bears only a few small granules. The upper surface of 

 the wrist is rather coarsely granulated, considerably flat- 

 tened and distinctly separated from the entirely smooth 

 and convex outer surface. The size of the larger chela is 

 somewhat variable; in some specimens it is twice as long 



Notes from the Leyden JMixseum, Vol. X.III, 



