352 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21 



Breeding: Egg-bearing females in August or September in the Gulf 

 of California. (Lockington) Eggs in November in Mexico and in Jan- 

 uary-March in Costa Rica. (Crane) Ovigerous females were encountered 

 by the Velero III in Costa Rica in February, in Panama in March, and 

 in the Gulf of California in May, and at Tiburon Island in June by 

 William Neil Smith, II. 



Remarks: Because of the existence of a paratype in the M.C.Z., a 

 neotype is not proposed for the species. Station 1092-40, Bahia Catalina, 

 outside Guaymas, is nearest to the type locality, Pinacate Bay. 



Genus MITHRAX Desmarest 



Mithrax Desmarest, 1823, p. 263. Milne Edwards, 1837, p. 83, pi. 27. 

 A. Milne Edwards, 1875, p. 91. Rathbun, 1925, p. 379. 



Trachonites Desmarest, 1823, p. 263; type: Cancer aculeatus Herbst, 

 1790= Mithrax pilosus Rathbun. 



Mithraculus White, 1847, p. 7; type: M. coronatus White, 1847 (not 

 Cancer coronatus Herbst) = Mithrax (Mithraculus) sculpt us (La- 

 marck). 



Nemausa A. Milne Edwards, 1875, p. 80; type: N. spinipes (Bell), 

 1836, by subsequent designation of Miers (1879c, p. 666). 



Type: The Atlantic Cancer aculeatus Herbst, 1790, a species now 

 recognized as Mithrax pilosus Rathbun, 1892, type of Mithrax Des- 

 marest by subsequent designation of Milne Edwards (1837). 



Description: Carapace convex and little elongate, narrowing notice- 

 ably in front. Front formed of two small, often pointed rostral horns, 

 with other preorbital or antennary spines or projections at the side. 

 Orbital margins generally more or less spinous or tuberculate. Basal 

 article of the external antennae wide, bearing in front two or three 

 strong spines ; second article inserted outside of the orbit, at the base of 

 the rostrum. Merus of the external maxillipeds broad and dilated on the 

 outside; exognath broad. Sternal plastron nearly circular. 



Chelipeds long and strong, especially in the male ; chelae deeply hol- 

 lowed into a spoon shape, and the fingers leaving between them, when 

 closed, a considerable space. Ambulatory legs robust, armed with spines, 

 and ending in hooked digits often armed with several spinules on their 

 inferior surface. 



Abdomen of the male formed of seven free articles. (A. Milne Ed- 

 wards, modified) 



