DESCRIPTION OF THEEE SPECIES OF CRABS (OSA- 

 CHILA) FROM THE EASTERN COAST OF NORTH 

 AMERICA. 



By Mary J. Ratiibun, 



Associate in Zoologif, Vniivd States National Museum. 



INTRODUCTION. 



A reexamination of the specimens of so-called Osachila fuherosa 

 in the United States National Museum discloses the presence of 

 three species instead of one in the area extending from Cape Hatteras, 

 North Carolina, to the Gulf of Mexico and the West Indies. The 

 species are very closely related and their ranges overlap. Through 

 the kindness of Dr. AValter Faxon and Prof. C. C. Nutting, I have 

 been permitted to study all the specimens in the Museum of Com- 

 parative Zoology and the Museum of the State University of Iowa. 



CHARACTERS COMMON TO OSACHILA TUBEROSA AND ITS ALLIES. 



Carapace octagonal. Six large protuberances: one mesogastric, 

 one metagastric (paired), one cardiac, one mesobranchial (paired). 

 Protuberances and lateral margins finely eroded, as if Avorm-eaten. 

 Lobes of front separated by a deep, closed or narrow Ijutton-hola 

 fissure. Antero-lateral margin (continued toward tlie buccal cavity) 

 finely dentate. Postero-lateral margin with four larger teeth or 

 lobes, including the one at the lateral angle. Maxillipeds, sternum 

 and bases of legs below, eroded. Chelipeds eroded. Upper margin 

 of mamis tridentate. Margins of legs thin, punctate. 



DIFFERENCES. ; . ' 



O. tulerosa and anfMlensis are similar in form, while the carapace 

 of semilevis has the antero-lateral inargin longer in proportion to 

 the postero-lateral, the postero-lateral margin being therefore more 

 transverse. 0. tuherosa and antUlensis have a small longitudinal 

 protuberance between the branchial and cardiac protuberances; O. 

 sem/tlevis has none. O. tuherosa and semilems have the cardiac 

 region subcircular in outline; in O. antUlenms this region is con- 

 tinued backward in a narrowed prolongation. On either side of the 



Proceedings U. S. National Museum, Vol. 50-No. 2138. 



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