240 GEOLOGICAL SURVEY OP THE UNITED STATES TERRITORIES. 



the preceding species by its small, distinct, regular, concentric costre, instead 

 of mere striae. 



Locality and position. — Moreau River, Dakota Territory; in the Fox 

 Hills group, or formation No. 5 ; and on the Yellowstone River, in beds con- 

 taining a blending of the fossils of that rock and the Fort Pierre group. 



CORBULIDiE. 



Genus CORBULA, Bruguiere. 



Synon.~Carbv.la, Brug. (1792), Encyc. Moth., pi. 230.— Lamarck (1799), Prorlr., 89; and (1801) Syst. Au. 

 137; also, Ann. du Mus., VIII, 465; and (1B18) Hist. Nat., V, 495.— Blainv. (1818), 

 Diet. Sci. Nat., X, 397.— Defr. (1818), ib., 398.— Neilsson (1827), Petref. Snec, 17.— 

 Desh. (1830), Eucyc. M6th., Ill, 7.— Sowerby, jr. (1842), Conch. Man., 2d eel., 122.— 

 Geinitz (1846), Grand. Vers*., 413.— Gray (1847), Proceed. Zool. So'j;', 191— H. and A, 

 Adams (1856), Gen. Recent Moll., II, 355, &c. 



Aloidis, MiiMf. (1811), Entwurf,67. 



Agina, Tint™ (1822), Brit. Bivalves, 54.— Latreille (1825), Fam. Nat. (Germ, ed.), 211.— Fleming 

 (1828), Brit. An,, 459.— G. B. Sowerby, jr. (1842), Conch. Man. (2d ed.), 00. 



Leniidium, De Crist, and Jan (1832), 8.— Villa (1841), Disp. Syst., 45. 



Pachydon, Gabb (1868), Am. Jour. Conch., IV, 198 (nol Pachyodon, Stutchberry, 1842, = Thalas- 

 sides, Berger, 1833; nor Pachyodon (written Paxyodon), Sebum., 1817, = Syria, 

 Lamarck, 1814). 



* AnisothyHs, Conrad (1871), Am. Jour. Conch., VI, 190. — II. Woodward (1871), Ann. Mag. N. H.- 

 (4th ser.), VII, 104.— Dall (1872), Am. Jour. Conch., VII, 90 (subgenus). 



Amsorhynclms (Con. MS.), Meek (1872), Hayden's Second Prelim. Report U. S. Geol. Survey Ter- 

 ritories, 293 (as a subgenus). 



Etym. — Corbula, a little basket. 

 Type. — Corbula sulcata, Lamarck. 



Shell subtrigonal, transversely-oval, or subpyriform, generally rather 

 thick, gibbous, inequivalve, the left valve being smaller than the other; 

 anterior outline mere or less rounded; posterior side closed, generally more 

 produced, sometimes subrostrate ; surface concentrically striate or costate, 

 and covered by an epidermis ; hinge with one prominent cardinal tooth in 

 front of the cartilage-pit in the right valve, and a projecting cartilage-process 

 in the left; rarely with a slight projection of the cardinal margin, resembling 

 a rudimentary posterior lateral tooth ; pallial sinus shallow or obsolete ; scar 

 of pedal muscle generally distinct from that of the anterior adductor. 



The foregoing diagnosis and synonymy include three sections that have 



* Mr. Conrad proposed the name AnUothyris, under the impression that Mr. Gabb's name, as cor- 

 rected to Pachyodon, could not be used, because it had been applied by Stutchberry to another genus in 

 1842; while Paxyodon of Sebum., used for another genus, would, when corrected, also become Pachyodon. 

 Stntchberry's name, however, is a synonym of Thalassidct*, Berger, 1833 ; while Schumacher's is also a 

 synonym of Hyria, Lamarck, 1*17. Consequently, the name Pachyodon would seem to have been free to 

 be used for a new genus at the time Mr. Gabb published, as has, I believe, since been noticed by Mr. 

 Conrad. » 



