156 Proceedings of the Biological Society of Washington. 



oblique in dorsal view than in formosensis, lower border smoothly margined; 

 upper border of palm without definite marginal line; fingers more gaping in 

 distal half than in the new species. 



Ilyoplaxi formosensis, sp. nov. 



Holotype. — Adult male, Cat. No. 54473, United States National Museum. 

 Washoshu, Taihoku, Formosa; collected by M. Maki, Feb. 25, 1918. 



Measurements. — Largest male, length of carapace 5.8 mm., greatest 

 width 8.8 mm., width at antero-lateral angles 8.2 mm., at posterolateral 

 angles above 8.2 mm., at postero-lateral angles below 8.5 mm. 



Description. — Upper orbital margin nearly transverse, sloping backward 

 very little. Carapace rough with distant clusters of fine granules; sides 

 convex; a right-angled tooth at antero-lateral angle; antero-lateral width 

 and superior postero-lateral width equal. Front broadly rounded, slightly 

 angled on each side. Male chelipeds large, margins finely granulate; fingers 

 long, immovable ones lightly deflexed, a broad tooth on dactyl occupies one- 

 third of gape. First and second ambulatory legs very hairy, collecting 

 mud ; shallow, ill-defined tympanum on merus of first three legs ; on first and 

 third legs it is of moderate size, on the second leg when the mud and hair is 

 removed the tympanum appears to occupy nearly the whole surface of the 

 article. Male abdomen slightly constricted between fourth and fifth seg- 

 ments, the fifth segment distinctly broader than long. 



Near I. tenella Stimpson,^ which is distinguished by a soft body and by 

 tympana occupying the entire surfaces of the merus. Otherwise, Stimp- 

 son's description of genus and species might apply to the new species. 



illyoplax Stimpson, Proo. Acad. Nat. Sci. Philadelphia, vol. 10, 1858, p. 98 [44], used 

 for Tympanomerus Rathbun, Proc. Biol. Soc. Washington, vol. 11, 1897, p. 164. 

 2Proc. Acad. Nat. Sci. Philadelphia, vol. 10. 1858. p. 98 [44]. 



