DESCRIPTIONS OF TWO N^EW SPECIES OF CRABS FROM 

 THE WESTERN INDIAN OCEAN, PRESENTED TO THE 

 NATIONAL MUSEUM BY DR. W. L. ABBOTT. 



By Mary J. Rathbun, 



Aid, DeparttiWHt of Murine liirertebratfs. 



A LARGE niiinber of crabs were recently collected by Dr. W. L. 

 Abbott at the islands north of Madagascar. Among them are two new 

 species, both of which represent lare and peculiar genera. The genus 

 Hypoccelus of the Cancrid;e can be distinguished by the oblong or oval 

 cavity beneath the anterolateral border of the carapace. Three species 

 have already been described: H. (jranuJatu.'i, (De Ilaan), from Japan, 

 H. diverticulatus, (Strahl) [^Cancer sculptuHj Milne-Edwards, not 

 Herbst], found sparingly from Japan to the Red Sea and Mauritius, 

 and H. punctains^ Miers, of which ;i single specimen is known, from 

 Torres Straits. 



The other new form in the Abbott collection is a member of the Thel. 

 phusan genus Decfce»?Vf, the type of which was described by Ililgendorf 

 from the adjacent African continent. This genus differs from other 

 Thelphusida^ in having the eiferent branchial channel prolonged to the 

 front, a character iu which it approaches the Oxystomata. 



HYPOCCELUS AliBOTTI, now species. 



Carapace shaped much as in H. pimctatm * and strongly lobulated as 

 in that species; but the second lobule near the anterolateral margin is 

 longer than wide, and the posterior margin of the cardiac region is 

 transverse and is distinctly separated from a small median lobule. The 

 surface is rough with blunt spiniform tubercles, which also border the 

 somewhat truncate frontal lobes and the prominent pr;eorbital pro- 

 tuberances. There is a spine at the inner suborbital angle. The, 

 pterygostomian cavity is suboval, wider at its inner than its outer end. 

 The anterior margin is straight for nearly its whole length and is 

 formed by the anterolateral margin of the carapace. The cavity is 

 crossed by two ridges nearly parallel to the anterior margin, the ante- 



* Miers, Crustacea, H. M. S. AJvvt, p. 206, pL xix, fig. B, 1884. 

 Proceedings National MiistMiin, Vol. X V^II— No. 979. 



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