86 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



PINNOTHERES CONCHARUM (Rathbun). 



Plate 20, figs. 3-6. 



concharum RATHBUN, Proc. U. S. Nat. Mus., vol. 16, 1893, p. 

 250 (type-localities, False Bay. San Diego County, California, from 

 mantle of Mya arcnaria, Cat. No. 17498, and Puget Sound, from Car- 

 dita borcalis) ; Harriinan Alaska Exped., vol. 10, 1904, p. 188, text-tig. 

 94, pi. 7, fig. 6. WEYMOUTH, Leland' Stanford Jr. Univ. Publ., Univ. 

 Ser. No. 4, 1910, p. 60. 



Diagnosis. Carapace almost hard, posterior margin transverse. 

 Anterior half of carapace, as well as chelipeds and legs, thickly 

 margined with hair. Dactyli of legs falcate, similar. 



Description. Carapace subpentagonal, a little wider than long, 

 almost hard, smooth, a faint sulcus behind gastric region; an- 

 terior and antero-lateral margins denned by a rim of coarse setae, 

 thickest and longest at antero-lateral angles; sides rounding gradu- 

 ally downward; posterior margin transverse, rimmed; front arcuate, 

 advanced. Eyes stout, in circular orbits. An- 

 tennae equal in length to half width of front. 

 Terminal joint of palp of maxilliped small, 

 attached to inner edge of propodus and, when 

 the maxillipeds are in place, it is hidden under 

 FIG. 42. PINNOTHERES the thin edge of the merus. 



Chelipeds stout, margined with a band of 

 OF MALE coarse setae, as are also the ambulatory legs. 

 Inner surface of palm swollen, hairy; palm 

 widening much to distal end, lower margin convex. 



Length of legs 2, 3, 1, 4, the second leg longest ; segments broad and 

 flat, anterior margin of propodi and posterior margin of first pro- 

 podus convex ; posterior margin of second propodus concave, of third 

 and fourth straight ; dactyli similar, falcate, slender, horny tips long 

 and very slender, making nearly half length of segment. 



Sternum and abdomen smooth, the latter bordered with hair; ab- 

 domen of adult male and immature female tapering rather regularly 

 from third to last segment, third, fourth and fifth partially fused, 

 seventh subquadrate with distal margin arcuate. Since this paper 

 was sent to the printer a large number of small specimens (50443) 

 have been received, of which the males have the abdomen widened at 

 the end, the terminal segment being wider than long, end truncate, 

 sides rounded, while the females have the tapering abdomen char- 

 acteristic of the large male. I am unable to detect other differences 

 in the two forms of the male. All the females known have a narrow 

 abdomen and are probably immature. 



