THE SPIDER CRABS OF AMERICA 411 



MITHRAX (MITHRAX) PLEURACANTHUS Stimpsoa 



Plate 150 



Mithrax pleuracanthus Stimpson, Bull. Mus. Comp. Zool., vol. 2, 1871, p. 

 116 (type-localities, Key West, 2-5 fathoms; Tortugas, 5 to 6 fathoms, 

 and St. Thomas; types not extant). — A. Milve Edwards, Crust. R6g. 

 Mex., 1875, p. 95, pi. 20, figs. 3-3/ (Guadeloupe).— Rathbun, Bull. U. 

 S. Fish Comm., vol. 20 for 1900, pt. 2 (1901), p. 68. 



Mithrax depressus A. Milne Edwards (part). Crust. Reg. Mex., 1875, p. 

 96, pi. 20, figs. 4-4 c (type-localities, Guadeloupe and Woman Key; figured 

 cotype from Guadeloupe in Paris Mus.; the cotypes from Woman Key 

 are in M. C. Z. and are young hispidus). — Rathbu.v, Bull. U. S. Fish 

 Comm., vol. 20 for 1900, pt. 2 (1901), p. 68. 



Mithrax hispidus Rathbu.v, Proc. U. S. Nat. Mus., vol. 15, 1892, p. 265 

 (part) . 



Diagnosis.— Oi the four lateral protuberances of the carapace, the 

 last is spiniform, the others tuberculated; second branchial tubercle 

 reduced in size. A small postero-lateral tubercle. Rostral sinus 

 V-shaped in the young, U-shaped in the old. 



Description. — The form of the carapace resembles that of the two 

 preceding species ; the third or posterior branchial spine is longer than 

 the first, however, and the second spine shorter than the first; there 

 are several tubercles about the base of each lateral spine. Tubercles 

 of carapace well marked. There is a small postero-lateral tubercle; 

 above it and further in there is a large tubercle which is one of a row 

 of two arranged almost transversely. Rostral horns shorter and 

 wider than in hispidus or carihhaeus, and interspace narrower and in- 

 clined toward the triangular; in the young, always triangular. The 

 arm of the cheliped bears usually either a simple spine or a spine 

 with a tubercle on its proximal slope. 



Color. — Carapace yellowish white, with blotches of bright red; the 

 2 largest red spots over branchial areas; a median spot on cardiac 

 area; a pair situated farther back; another small pair behind orbits, 

 another beneath orbits; legs yellowish white, blotched or barred with 

 red; chelae light red with pale tips. (Verrill, for depressus.) 



Measurements. — ^Largest specimen, male (46815), total length of 

 carapace 36.3, width without spines 38.2, with spines 43, length of 

 propodus of cheliped 31.8, width of same 11.8 mm. 



Variations. — ^In the young the rostral horns are wider behind and 

 flatter than in the adult; in one of the largest males (46791), the 

 rostral sinus is rounded behind so that it appears almost U-shaped. 



In a small ovigerous female (50364), the large tubercle above the 

 postero-lateral margin has a sharp point, giving it a spinous appearance, 

 but its position is too high up to correspond to the spine of hispidus. 



Range. — From North Carolina and the Bahamas to Gulf of Mexico 

 and Caribbean Sea. Shallow water to 28 fathoms. 



Material examined. — See table, pages 412-417. 



