Vol. 33, pp. 23-24 July 24, 1920 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



NEW SPECIES OF SPIDER CRABS FROM THE STRAITS 

 OF FLORIDA AND CARIBBEAN SEA. 1 



BY MARY J. RATHBUN. 



These species will be more fully described in a bulletin on 

 American spider crabs in preparation. The two species of 

 Mithrax belong to the group of M. hispidus 2 in which the 

 carapace is broad-ovate and more or less lumpy and the mar- 

 ginal spines more or less complex, either with a secondary 

 spine or accessory tubercles. 



Mithrax caribbaeus, sp. nov. 



Holotype. — Adult male, Cat. No. 50363, United States National Museum. 

 Collected in the harbor of St. Thomas, West Indies, from piles near the 

 town, by C. R. Shoemaker, July 7, 1915, and given to the National Museum 

 by the Carnegie Institution. 



Measurements. — Male holotype, total length of carapace 66.3 mm., 

 width without spines 71.3 mm., with spines 78.4 mm. 



Description. — On the postero-lateral margin there is a tubercle which 

 forms the outermost unit of a transverse row of three tubercles on the 

 dorsum, this row being subparallel to another anterior row of three tuber- 

 cles. Rostral sinus u-shaped, about as wide as each horn; horns longer 

 and less truncate than in M. hispidus. Two stout spines on anterior mar- 

 gin of arm. Crenulation of prehensile edges of fingers persisting in the 

 old. 



Mithrax tortugae, sp. nov. 



Holotype. — Immature female, Cat. No. 50442, United States National 

 Museum. Collected at the Tortugas, Florida, by W. H. Longley, 1917. 



Measurements. — Female holotype, total length of carapace 19.7 mm., 

 width without spines 22.1 mm., with spines 24.3 mm. 



1 Published by permission of the Smithsonian Institution. 



2 Cancer hispidus Herbst, Natur. Krabben u. Krebse, vol. 1, 1790, p. 245, pi. 18, 

 fig. 100. 



3— Proc. Biol. Soc. Wash., Vol. 33, 1920. (23) 



