Boone, Crustacea, Cruises of "Eagle" and "Ara," 1921-28 93 



by dressing its slender, hairy, color-barred legs with fragments of its 

 environment — hydroid, sand grains, bryozoa, etc., rendering the legs 

 exceedingly inconspicuous, while the rugose, pebble-like carapace 

 looks like a bit of coral rock. It moves very rapidly and is difficult to 

 catch as it scuttles into a crevice of the rock when disturbed. 



Technical descriptions : Carapace compressed, pyrif orm, about as 

 wide as long, areas clearly delineated, rostral horns short and wide, 

 more V- than U-shaped; anterolateral border with four dentitions, 

 the first three of which are tuberculate, the fourth, spiniform; one 

 postlateral tubercle. There are a pair of small submedian tubercles 

 in the frontal region in line with the preorbital angle; behind these 

 are a similar, larger pair of tubercles which in turn are followed by 

 a transverse row of five tubercles in the gastric region; posterior to 

 this row is a single tubercle placed between the horns of a lunate series 

 of rugosities which border the urogastric line. The branchial region 

 is coarsely tuberculated and the cardiac region only a little less so. 

 The chelipeds are a trifle less robust in the female than in the male ; 

 the merus of the chelipeds has a single tubercle; the fingers are 

 slightly gaping but meet closely at the tip. The ambulatories are sub- 

 similar, slender, hairy. The specimens which have come under my 

 observation range from 10 to 20 mm. long. 



Synonymy. — Mithrax pleuracanthus Stimpson, Bull. Mus. Comp. 

 Zool., vol. 2, p. 116, 1871. — ^A. Milne Edwards, Crust. Reg Mex., 

 p. 95, pi. 20, figs. 3-3f, 1875.— Rathbun, Bull. U. S. Fish. Comm., 

 vol. 20, pt. 2, p. 68, 1901 ; BuU. 129, U. S. Nat. Mus., p. 411, pi. 

 150, 1925. 



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

 95, pi. 20, figs. 4-4c, 1875.— Rathbun, Bull. U. S. Fish. Comm., 

 vol. 20, pt. 2, p. 68, 1901. 



Mithrax hispidus Rathbun, Proc. U. S. Nat. Mus., vol. 15, p. 265 

 (part), 1892. 



Mithrax (Mithrax) pleuracanthus Rathbun, Bijdragen tot de Dier- 

 kunde, Natura Artis Magistra te Amsterdam, Aflev. 23, p. 20, 

 1924. 



Mithrax (Mitlirax) acuticornis Stimpsou. 



Plate 29, fig. A. 

 Name : Sharp-horned Mithrax. 



Diagnostic characters: Small, orange, red, body elongate-pyri- 

 f orm, with spinulose upper surface ; four anterolateral spines of which 



