THE SPIDER CRABS OF AMERICA 431 



MITHRAX (MITHRACULUS) FORCEPS (A. Milne Edwards) 



Plate 156 



Mithraculus forceps A. Milne Edwards, Crust. Rdg. Mex., 1875, p. 109 , 



pi. 23, fig. 1 (type-locality, Guiana; type in Paris Mus.). 

 Mithraculus hirsutipes Kingsley, Proc. Boston Soc. Nat. Hist., vol. 20 



1879, p. 147 (type-locality. Key West, Florida; type not extant). 

 Mithrax forceps Miers, Challenger Rept., Zool., vol. 17, 1886, pp. 87 and 



88.— Rathbun, Proc. U. S. Nat. Mus., vol. 15, 1892, p. 269. 

 Mithrax hirsutipes Miers, Challenger Rept., Zool., vol. 17, 1886, p. 87. 

 Mithrax forceps hirsutipes Verrill, Trans. Conn. Acad. Arts and Sci., vol. 



13, 1908, p. 409, text-fig. 42, pi. 24, figs. 4-6. 



Diagnosis. — Ridges between sulci of carapace little subdivided. 

 Four acute antero-lateral spines or teeth. Wrist smooth above. 

 Color reddish or yellowish. 



Description. — Carapace similar in shape to that of J/, sculptus, 

 comparatively smooth, large specimens with scattered punctures, 

 small ones deeply sculptured. Three grooves Tun diagonally back- 

 ward from near first, second, and fourth sinuses of lateral margin; 

 of the intervening ridges thus formed, the two anterior are less 

 broken up into lobules than in M. sculptus. Six or seven depressed 

 tubercles along margin and on posterior part of brancliial region, 

 two or three along outer margin of hepatic region, and two pairs on 

 frontal region directly behind lobes of rostrum. Median notch of 

 front broadly V-shaped. Antero-lateral teeth four, acute, slender, 

 separated by broad rounded sinuses, the first the shortest and in 

 large specimens subacute, the remainder sharp and directed forward, 

 the second usually the longest and largest. Sometimes a small 

 postero-lateral tooth. 



Arm with five spines or spiniform tubercles on upper (posterior) 

 margin, two on upper face just within margin; on the inner (anterior) 

 margin two prominent teeth. Carpus smooth, sometimes unarmed, 

 often with a short spine or tubercle on inner margin anterior to inner 

 angle, giving appearance of a double tooth. Fingers widely gaping 

 in male; dactylus with a large tooth one-third distance from proximal 

 end, or instead a few minute teeth; the poliex may have from one to 

 three small teeth or tubercles in the middle. Ambulatory legs 

 distinctly spiny and fine-hairy. 



Color. — Chestnut or terra-cotta or uniform yellowish-brown, vary- 

 ing to dull yellow and to greenish-browTi. Often there is a wide, 

 pale yellow, median dorsal stripe, especially in the young, where 

 also the legs are often banded. (Verrill.) 



Habitat. — On rocky shores and reefs in crevices and living under 

 stones and dead corals; also exposed, between tides and in shallow 

 water. (Verrill.) 



Measurements. — Male (25448), entire length 21, width 24.6 mm. 



