PROCEEDINGS OF THE NATIONAL MUSEUM. 121 



arcli of the base cut into three subeqnal parts by two especially strong 

 ridges (corresponding- to channels on the brachial valve), between whicli 

 the surface of the valve may be more or less ribbed radially, but is 

 always flattened or depressed, corresponding to an upward flexure of 

 the basal margin ; teeth strong, supported by deeply receding buttresses; 

 no medial septum; the adductors with widespread ends, rather distant 

 from the medial line, confined to the upper third of the valve; paliial 

 sinuses large, divaricating near the margin from five principal trunks 

 on each side; the genital glands yellowish, extending in narrow bauds 

 along the sinuses nearly to their furcation ; peduncle short, dark brown ; 

 brachial valve flatter, with a wide, low cardinal process, little promi- 

 nent; teetl) strong without buttresses, medial septum short, very thin 

 and high, subtriangular; brachidiujn unusually slender; paliial sinuses 

 numerous, much branched with a medial trunk nearly reaching the 

 margin. Height of average specimen 30; width 30, diameter 17 mm. 

 Old specimens attain a larger size. One dead pedicle valve measures 

 47 mm. high, 43 wide, and 20 mm. deep. 



The varied forms which the brachidiuni assumes during development 

 have been fully illustrated and described by Beecber in the paper 

 already cited. The first specimens received were in j)oor condition, 

 and it was thought possible that the species might be identical with 

 T. occidentalis. Subsequently a fine lot of material from the vicinity 

 of Cerros Island showed that the two species were perfectly distinct. 

 T. ohsoleta has no very near relative in the North Pacific. The colors 

 recall the T. coreanica, Laqueus pictits, and FrenuUna sanguinea, all 

 quite distinct as to form. In form the nearest species is the T. ruhuji- 

 nosa, Dall, which is only known from the type in the National Museum, 

 collected by the United States Exploring Expedition, and labeled as 

 from the Cape of Good Hope. It is possible that this locality is erro- 

 neous, but the species has a diflerent sculpture from T. ohsoleta, and 

 has only a faint reddish suflusion in the general brownish coloration. 

 The peculiarly slender, rather wide, and arched brachidium is some- 

 what similar in the two species. It should be said that an occasional 

 specimen of T. ohsoleta has the foramen completed by a junction of the 

 deltidia. T. ruhiginosa is figured for comparison. PI. xxx, figs. 3, 4. 



TEREBRATALIA TRANSVERSA, S o w e r b y . 

 Plate XXXI, figs. 12, 13. 



Terehrafiila transi-ersa, Sowerby, Thes. Couch., i, p. 2G1, pi. Lxvii, figs.lU-115, 



1846. Not of Gould, 1860. 

 Terehratella transversa, Dall, Sci. Res. Expl. Alaska, p. 47, 1877; Proc. Acad. Nat. 



Sci. Phila., 1877, p. 157; Davidson, Mod. Rec. Bracli., p. 79, pi. xvi, tigs. 6-12, 



14, 14«, 1887 (exiuirte). 

 Terehratnla caurina, Gould, Proc. Bost. Soc. Nat. Hist., iii, p. 347, 1850; Moll., U. S. 



Expl. Exp., p. 468, pi. XLiv, fig. 582, 1852. 



Stations 2858, 2961, 2904, etc., in 10 to 230 fathoms, from the Aleutian 

 Islands to Catalina Island, California. Oregon, United States Exxilor- 

 ing Exi)e(lition. 



