THE SPIDEK CRABS OF AMERICA 403 



MITHRAX (MITHRAX) BEIXD Gerstaecker 



Plates 142 and 143 



Mithrax ursus Bell, Proc. Zool. Soc. London, vol. 3, 1835 (1836), p. 171, 

 Galapagos Islands (not Cancer ursus Herbst, 1788); Trans. Zool. Soc. 

 London, vol. 2, 1836, p. 52, pi. 10, figs. 2, 2c, 2d, 2e, and 3.— A. Milne 

 Edwards, Crust. Reg. Mex., 1875, p. 103. 



Mithrax bellii Gerstaecker, Arch. f. Naturg., vol. 22, pt. 1, 1856, p. 112; 

 name substituted for M. ursus Bell, not (Herbst); (type-locality, that 

 given by Bell, namely, Galapagos Islands; type not extant). 



Diagnosis. — Size large. Dorsum closely paved with flat granules. 

 Projections of margin lumpy. Wrist tuberculate above, five tubercles 

 on inner margin. 



Description. — The adult is almost devoid of hair; the carapace is 

 convex, broadly ornate, a little broader than long. Surface covered 

 with flattened granules and very unequal tubercles, so closely crowded 

 that they form a continuous pavement. Margins thick, projections 

 coarsely rounded. Rostrum with two thick, rounded horns sepa- 

 rated by a V-shaped space, and two pairs of dorsal tubercles. The 

 knob at the angle of the basal antennal article is curved, larger than 

 either rostral horn and on a higher level. Preorbital lobe tuberculi- 

 form, not prominent. Orbital margin with two other, smaller 

 tubercles above, one, not prominent, at outer angle, and one below, 

 besides a submarginal tubercle or blunt spine on the basal antennal 

 article, which is conspicuous in dorsal view. Just behind and between 

 the orbits there are two longitudinal rows of 2 or 3 tubercles each, 

 and further back a transverse, sinuous line of five tubercles. On the 

 lateral margin are six tubercles, the first and second large and bearing 

 an accessory, anterior tubercle, the first hepatic, the second largest 

 of all, the third is largest of the simple tubercles, the fourth the 

 smallest, the sixth is postlateral. Further back on the postlateral 

 margin there is a row of minor tubercles. On the subbranchial, sub- 

 hepatic, and suborbital regions there is a row of tubercles some of 

 which are visible in a dorsal view. Pterygostomian ridge tuberculate. 



On the anterior margin of the merus of the outer maxilhped there 

 is a strong, depressed spine, pointing obliquely inward. Chelipeds 

 of male strong; arm tuberculate above, two blunt spines or tubercles 

 on inner margin and six of the same on outer margin; wrist covered 

 with low knobs, inner margin with a row of five knobs; hands elon- 

 gate, arcuate above, concave below; fingers moderately gaping, tips 

 w^th edges finely crenulate, a strong tooth near base of dactyl, edge 

 of fixed finger finely denticulate part w^ay in the gape. Legs stout, 

 three principal articles tuberculate above, especially on the margins; 

 of dactyls dark colored for nearly a third their length. 



Abdomen of male verv wide, last segment with concave sides. 



