102 CALIFORNIA ACADKMV OF SriF.XCES. 



valve with twciity-oijjlit square topped, rather narrow, radial ritlncs, separated by slinlitly narrower 

 interspaces; cardinal area triangular, broad, faintly sculptureil with parallel lines transverse to liinjje 

 line; two nearly equal series of teeth, crowded in middle, becominjf slightly oblique and further 

 separated at the distal enils; niarj^ins serrate. 



Dimensions. — I.onj;. 28 mm.; alt. 26 mm.; distance between dorsal and ventral margins 

 20 mm.; umbo to anterior extremity 11 mm.; to posterior extremity 17 mm. 



I liis i.-i (Ik- only Area so tar nported from tlic Pleistocene of the Pacific Coast. 

 It lias been reported l»y C'urpoiiter as being one of the few species common to l)otIi 

 tiiL' West Indian and Pacific (Panama) faunas. This species and IUppomjc antiqud- 

 lus, which Carpenter considers eqnal to //. mitnila of the West Indian fauna, are the 

 only two species which occur in the Pleistocene of San Pedro and the living fauna of 

 the West Indies. These two species ofler no proof ofaclo.se water connection be- 

 tween these two regions during Pleistocene time, for the occurrence in both regions 

 of these two species is merely accidental, or a coincidence. The specimen described 

 was identified by Dr. Dall. 



Rare in the upper San Pedro series of San Pedro; two specimens, a right and 

 a left valve. The specimen figured is from llic upi)er San Pedro series at San Pedro, 

 and is now in the collection of Delos Arnold. 



Living. — Gulf of California; Central .Vnicrica; West Indies (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



Superfaniily OSTRACEA. 



Family \"1I1. OSTREID.E. 

 Genii.-j Ostrea (Liane) Lamarck. 



Shell irregular, attached by the left valve; upper valve fiat or concave, often plain; lower 

 conve.\, often plaited or foliaceous, and with a prominent beak; ligamental cavity triangular or 

 elongated; hinge toothless, structure subnacreous, laminated, with a prismatic-cellular substance 

 between the margins of the laminae. 



Type, Ostrea ednlis Lin no. 



22. Ostrea lurida Carpenter. 



Oslrea lurida CpR., Brit. Assn. Rept., 1863, p. 645; Jour, de Conch., Vol. XII, 1865, p. 137. Gabb, 

 Pal. Cal., Vol. II, 1869, p. 106. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 256. Keep, 

 West Coast Shells, p. 164, 1892. Wit-MAMSON, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 193. 

 Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 4, 1898, p. 687. 



Shell of medium size, irregular, suborbicular, ellipsoidal, or elongated; surface laminated and 

 sometimes irregularly plaited; beak prominent; hinge toothless. 

 Dimensions. — Long. 35 mm.; alt. 50 mm. 



rjratles into two varieties, e.rpnm^n Cpr., which is nearly circular, and rufoides 

 C'pr., which is of a reddish hue on the interior. Specimen identified by Dr. Dall. 



