THE SPIDER CRABS OF AMERICA 



391 



Comparison of Mithrax acuticornis tvith spinosissimus and cornutus 



sptnostsstmug, young 



Two well-developed spines on 

 lower margin of orbit between 

 outer spine and antennal segment. 



No spine on bassil antennal seg- 

 ment at articulation of next seg- 

 ment. 



Carapace without lateral angle; 

 the antero-lateral and postero- 

 lateral margins curve gradually 

 into each other. 



The fifth lateral spine, counting 

 the hepatic as the first, is in line 

 with the gastro-cardiac suture. 



acuticoTftis 



One spine and a shallow lobe, 

 sometimes spine-tipped, on lower 

 margin of orbit between outer 

 spine and antennal segment. 



A small, sharp spine on basal 

 antennal segment at articulation 

 of next segment. 



Carapace with a lateral angle 

 formed by the meeting of the 

 antero-lateral and postero-lateral 

 margins, and armed with one of 

 the longest marginal spines. 



The fourth lateral spine is a 

 little behind the line of the gastro- 

 cardiac suture. 



cornutus, young 



Two well-developed spines on 

 lower margin of orbit between 

 outer spine and antennal segment. 



A small, sharp spine on basal 

 antennal segment at articulation 

 of next segment. 



Carapace with a lateral angle 

 formed by the meeting of the an- 

 tero-lateral and postero-lateral 

 margins and armed with one of , 

 the longest marginal spines. 



The fourth lateral spine is a 

 little behind the line of the gastro- 

 cardiac suture. 



MITHRAX (MITHRAX) SPINIPES (Bell) " 



Plate 136, fig.s. 3 and 4; plate 262, fig. 5 



Pisa spinipes Bell, Proc. Zool. Soc. London, vol. 3, 1835 (1836), p. 171 

 (type-localities, Galapagos, 16 fathoms (male); St. Elena, 6 fathoms 

 (female); types not extant); Trans. Zool. Soc. London, vol. 2, 1836, p. 50, 

 pi. 9, figs. 6, 6.9, 6/, 6u. 



Nemausa spinipes A. Milne Edwards, Crust. Reg. Mex., 1875, p. 82. 



Mithrax {Nemausa) spinipes Miers, Challenger Rept., Zool., vol. 17, 1886, 

 p. 85. 



Diagnosis. — Small. Horns long. Hepatic and first branchial 

 spine single. Two small spinules side by side on anterior mesogastric 

 region. 



Description. — Carapace similar to that of 31. acuticornis, having a 

 lateral angle at which is situated a prominent spine a little below the 

 level of the other marginal spines; as in that species, there are 5 lateral 

 spines besides the orbital, the last and smallest being postlateral; the 

 hepatic and the first branchial spine are single, not double as in 

 acuticornis. On the anterior part of the mesogastric region and a 

 little in front of the line of 4 protogastric spines, there are two small 

 spinules side by side instead of a single one, as in acuticornis. The 

 spines of the rostrum, orbits, and basal antennal segment correspond 

 to those of acuticornis. The small and immature male examined 

 shows several spines on the dorsal surface of the \\Tist but none on 

 the inner margin and none on the upper edge of the palm. Legs 

 much as in acuticornis. 



Measurements. — -Male (16064), entire length of carapace L3, length 

 from base of rostral horns 11, width without spines 8.2, with spines 

 10.3 mm. 



Range. — From Gulf of California to Galapagos Islands and St. 

 Elena, Ecuador. Depth, 6 to 33 fathoms. 



Material examined. — Gulf of California; lat. 24° 55' 15" N.; long. 

 110° 39' 00" W.; 33 fathoms; fne. gy. S. brk. Sh.; temp. 64.5°; sta- 

 tion 3001, Str. Albatross; 1 male immature (16064). 



" If Cancer spinipes Herbst (Naturg. Krabben u. Krebse., vol. 1, 1790, p. 239, pi. 17, flg. 94) be a Mithrax, 



then Bell's species needs a new specific name. 



