384 BULLETIN 129^ UNITED STATES NATIONAL MUSEUM 



ment, the outer one small and acute, the inner one sunilar to the ros- 

 trum but a little more advanced, and bearing a secondary spine or 

 spinule on the outer side near the end. Six spines on lateral margin, 

 the first two double, the first one occupying the hepatic region, the last 

 one smallest and on the postero-lateral margin. One suborbital, two 

 large subhepatic, and numerous subbranchial spines, besides one at 

 the angle of the buccal cavity and a row of three on the pterygosto- 

 mian region. 



Chelipeds of male massive, much longer than legs; merus armed 

 with numerous stout spines, of which eight or nine are on the outer 

 margin, the rest irregularly disposed; carpus dotted with unequal 

 spines of which about 5 are on the inner margin; manus high, com- 

 pressed, armed above with a more or less double row of spines; and 

 on the inner surface with two to four spines on the proximal half. 

 In the old males the spines of the cheliped tend to become blunt 

 and tuberculiform, those of the arm retaining their spinous character 

 the longest. Fingers curved, leaving a wide gape, in the middle of 

 which is a strong tooth on the dactyl. Tips with crenated edges 

 behind which are a few low tubercles. 



Legs spinous and coarsely hairy, hair most dense on the last 

 2 segments; propodus very elongate and compressed. 



Chelipeds of adult female no longer and not much stouter than 

 legs of first pair; manus tapering a little distally; fingers narrowly 

 gaping, with numerous denticles on the prehensile edges. 



Medium-sized specimens. — The carapace is relatively longer, all 

 the spines are sharper than in the old, the rostral horns curve inward 

 at the tips which are sharp; the carapace is short-hairy; the chelipeds 

 of both sexes are small, the gape occupies only about half length of 

 fingers. 



Young. — The last-mentioned characters are exaggerated, the 

 rostral horns are relatively much longer and slender, being about 

 one-fifth as long as remainder of carapace, two spines on the sub- 

 orbital margin outside the antennal segment, the chelipeds are no 

 longer or stouter than the last pair of legs, the gape of the fingers is 

 reduced. 



Coloi\ — Vinous red with yellowish tints (A. Milne Edwards). 

 Bright carmine (A. H. Verrill). Thorax dark red, ambulatories 

 brick red, chelipeds rose red with yellow fingers (Doflein). 



Measurements. — This is the largest species of Mitlirax. Male 

 (41777), entire length of carapace 170, length exclusive of horns 

 163, width just in front of fourth branchial spines 167, width between 

 tips of fourth branchial spines 174, greatest width across subbranchial 

 regions 184, length of manus below 187, above 97, greatest height of 

 manus, including tubercle, 74.3 mm. 



