66 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Mithrax acuticornis Stimpson. 
Mithrax acuticornis Stimpson, Bull. Mus. Comp. Zool., ir, 116, 1870; A. Milne Edwards, Crust. Rc5g. Mex., 98, 1875. 
Mithrax ( Nemausa ) acuticornis Rathbun, Proe. U. S. Nat. Mus., xv, 260, pi. xxxvii, f. 1, 1S92. 
Nemausa rostrata A. Milne Edwards, Crust. Reg. Mex., 81, pi. xvn, f. 4, 1875. 
Carapace longer than broad, armed especially on posterior and lateral portions with sharp spines 
and spinules. Antero-lateral margin with four slender, sharp spines, the first three of which have a 
smaller anterior spine; a short postero-lateral spine. Rostral horns in large specimens two-fifths as 
long as remainder of carapace, in small specimens relatively shorter; slender, acuminate, diverging. 
Preorbital spine acute, obliquely ascending; postorbital spine equally long; two shorter spines above 
and two below the orbit. Antennal joint with a long antero-external spine, a third or more as long as 
the rostrum; an outer spine much shorter; a third but extremely short spine at the base of the second 
joint. Arm and wrist armed with very sharp spines; hand smooth. Meral and carpal joints of 
ambulatory legs spinous, the spines forming two marginal rows on upper surface. 
This species has a strong resemblance to young M. spinosissimus. 
Dimensions of male: Entire length of carapace, 21.4 mm.; entire width, 14.2 mm. 
Gulf of Mexico and Caribbean Sea, 12 to 121 fathoms; Bermudas. Mayaguez Harbor, 25 to 30 
fathoms, station 6062, 1 young female. 
Mithrax spinosissimus (Lamarck). 
Maia spinosissima Lamarck, Hist. Nat. Anim. sans Vert., v, 241, 1818. 
Mithrax spinosissimus Milne Edwards, Mag. Zool., ii, pis. 2 and 3, 1832. 
Carapace covered with spines more or less elongate, which tend to disappear in very large indi- 
viduals; surface between spines smooth. Rostrum formed of two short and slightly divergent horns. 
Preorbital spines sharp and directed a little upward. Two spines on basal article of external antennae. 
Orbital border cut into five or six additional spines. Antero-lateral margin armed with five or six 
large spines, of which the first two are bifurcate. Chelipeds very large. Arm and wrist spiny. The 
upper border of the hand has a double row of spines, which become blunt or tuberculiform with age; 
the inner face has two or three tubercles near the wrist. Ambulatory legs very spinous. Merus of 
external maxillipeds deeply cut at its inner angle. 
Color, vinous red, with yellowish tints (A. Milne Edwards). 
Dimensions of male: Entire length, 131.4 mm. ; entire width, 136 mm. This is the largest species 
of the genus. Young specimens are more elongate (longer than broad) and have longer horns. 
Bahama Banks; Florida Keys; West Indies. Bayamon (Gundlach); San Juan (G. M. Gray). 
Mithrax pilosus Rathbun. 
Cancer aculeatus Herbst, Natur. Krabben u. Krebse, I, 248, pi. xix, f. 104, 1790. (Not C. aculeatus O. Fabricius, 1780.) 
Mithrax aculeatus Milne Edwards, Mag. Zool., n, 1832. 
Mithrax pilosus Rathbun, Proc.. U. S. Nat. Mus., xv, 262, pi. xxxix. 1892. 
Carapace wider than long in specimens of large size, but in small specimens the length and width 
are more nearly equal. It is covered, as well as the legs, with plumose set®, which are crowded and 
conceal the surface; when removed, they disclose flattened granules. Carapace also furnished with 
spinose tubercles as follows: Three, small, arranged longitudinally each side of median line just behind 
rostrum; four transversely on gastric region in two distant pairs; one further back on median line of 
gastric; three forming a triangle on cardiac; nine or ten scattered on each branchial region; four in an 
arcuate row above posterior margin. Lateral spines five (the fifth postero-lateral), stout, triangular, 
tips hooked forward, the first ones often double or triple, especially in specimens of large size. Rostral 
horns strongly incurved at tips. Preocular spine prominent, upturned. Three other orbital teeth — one 
above, one below, one external. Basal antennal joint with a long antero-external spine, hooked 
inward; on outer margin a triangular tooth; another at insertion of second joint. Chelipeds large; 
arm and wrist very spiny ; hand with a few tubercles or spines on superior margin near wrist. Ambu- 
latory legs stout; meral and carpal joints spiny. 
Dimensions of male: Entire length, 113.2 mm.; entire width, 124 mm. 
Bahamas; Florida Keys to Venezuela; West Indies. Porto Rico: Reefs at Guanica; reefs at 
Ponce; Culebra; Aguadilla (Gundlach). 
