32 BULLETIN 138, UNITED STATES NATIONAL MUSEUM 



(pi. 4, fig. 5), lower margin with a tooth at inner end (pi. 5, fig. 2). 

 Basal article of antennules swollen (pi. 5, fig. 2). Chelae of female 

 narrow, strongl}' arcuate, fingers longer than palm, very slender, 

 grooved, edges meeting, their teeth low (pi. 5, iigs. 2 and 3) . Cheliped 

 remote from first ambulatory (pi. 5, fig. 3). 



Measurernents. — Holotype female, length of carapace 24.5 mm., 

 width 34.5 mm., width between anterior angles 27.5 mm. 



Occurrence. — California; Bolsa Point, 1 mile north of Pigeon 

 Point, San Mateo County; Loo. 27, Santa Cruz quadrangle; Chico 

 formation, upper Cretaceous series. Holotype, adult female (Cat. 

 No. 31069, U. S. N. M.) ; paratypes, one immature female, one male. 



Family GRAPSIDAE Dana 



Carapace usually quadrilateral, lateral borders either straight or 

 slightly arched, orbits at or near antero-lateral angles, front broad. 

 Buccal cavern square; generally a gap between outer maxillipeds; 

 the palp articulates either at antero-external angle or at middle of 

 anterior border of merus. Interantennular septum broad. Division 

 of orbit into two fossae accented. Male openings sternal. 



Genus HEMIGRAPSUS Dana 



Hemigrapsus Dana, Amer. Journ. Sci., ser. 2, vol. 12, 1851, p. 288; type, 

 H. crassimanus Dana. — Rathbun, Bull. U. S. Nat. Mus., No. 97, 1918^ 

 p. 264. 



Carapace transverse, quadrate, antero-lateral margin rounded and 

 dentate; an oblique ridge runs inward and backward from postero- 

 lateral margin. Chelipeds stout, subequal; fingers hollowed out on 

 the prehensile surface. Sternum much wider than base of abdomen. 



Pliocene — Recent. Not before found fossil. 



HEMIGRAPSUS. species 



Plate 7, fig. 3 



Description. — The great width of the sternal segments indicates 

 one of the Grapsidae and in particular the genus nemigraj^sus., two 

 of whose species are now very abundant on the Pacific coast of North 

 America. The first sternal segment is coarsely punctate, the second 

 and third are finely punctate on the posterior half, while a fcAV 

 granules are scattered over the wdiole surface. Third, fifth, and sixth 

 abdominal segments granulate. The depressions between the seg- 

 ments in the actual crab are here represented by ridges and the 

 abdomen is below the level of the sternum, or the reverse of the 

 position in the crab. The impression of a manus embraces appar- 

 ently the inner surface, which is coarsely punctate except near the 



