136 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.21 



anterointernal angle. Chelipeds in male much elongated, somewhat en- 

 larged ; palm long, compressed and distally widened. Ambulatory legs of 

 moderate length, slender, and decreasing regularly in length. Abdomen 

 composed of seven distinct segments. (Rathbun) 



The admission to the genus of a second species, Oregonia bifurca 

 Rathbun (1902a), in which the rostral spines are divergent rather than 

 contiguous, called for modification of the original description of Dana 

 (1851a), perpetuated by Holmes (1900) and Schmitt (1921). This was 

 done most acceptably by Rathbun (1925, above), although without 

 mention of the broad terminal male abdominal segments common to both 

 species and to O. mutsuensis Yokoya (1928). 



The superficiality of the similarity to Eurypodius Latreille, mentioned 

 in Dana's description and referred to in subsequent accounts, which 

 conveniently ignores this salient feature of the male abdomen, was exposed 

 by Balss (1929), who removed Latreille's genus from its time-honored 

 position next Oregonia in the systematic arrangement and placed it 

 following Macrocheira De Haan in the most primitive section of the 

 subfamily Inachinae. The male first pleopod with its filamentous appur- 

 tenances suggests that Oregonia finds its true relationship with Hyas 

 and Chionoecetes, with them forming a natural group of circum-Arctic 

 distribution, of which Oregonia, with its more open orbits, is the primi- 

 tive member. 



Range: From Bering Sea to Monterey Bay, California. Shallow 

 water to 764 fathoms. Occurs also in Japan. 



Key to the Pacific American Species of Oregonia 

 la. Rostral horns long and parallel. Postorbital spine remote from 

 eye, lanceolate, outwardly directed. Carapace narrow at hepatic 

 level. Dactyls of ambulatory legs short and stout. . gracilis 

 lb. Rostral horns short and divergent. Postorbital spine close to 

 eye, triangular, forwardly directed. Carapace wider at hepatic 

 level. Dactyls of ambulatory legs long and slender. . bifurca 



Oregonia gracilis Dana 

 Plate I, Fig. 2; Plate 10; Plate 11, Fig. 1 



Oregonia gracilis Dana, 1851a, p. 270; 1852, p. 106; atlas, 1855, pi. 3, 

 figs. 2a-c. Stimpson, 1857b, p. 456. Spence Bate, 1866, p. 269. 

 Lockington, 1877c, p. 74. Miers, 1879c, p. 646. S. I. Smith, 1880, 

 p. 209. Newcombe, 1893, p. 21 ; 1898, p. 76. Rathbun, 1894, p. 59; 

 1904, p. 171; 1925, p. 71, pis. 24, 25, text-figs. 19, 20. Caiman, 

 1898, p. 260. Walker, 1898, p. 274. Doflein, 1899, p. 183. Holmes, 



