110 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Tol.Y. 



Position and locality. — Jura-Trias strata, member of the foregoing 

 section; Southeastern Idaho. Collected by Dr. A. 0. Peale. 



AvicuLOPECTEN ALTUS White. — Shell, exclusive of the ears, sub- 

 ovate in marginal outline ; axis almost perpendicular to the hinge-margin, 

 or having a very slight backward obliquity ; hinge-margin shorter than 

 the greatest transversa diameter of the body of the shell. Eight valve 

 depressed-convex, the convexity being nearly uniform in all parts, except 

 the umbonal region, where it is, as usual, greatest ; beak small, moder- 

 ately narrow, pointed, and projecting very slightly above the hinge-mar- 

 gin; anterior ear moderately large, its anterior iDoint extending about 

 as far forward as the front of the shell, not \^ery distinctly separated 

 from tbe body of the shell, its anterior border broadly and not deeply 

 notched ; front margin nearly straight from the shallow notch of the 

 anterior ear to a i)oint a little below the mid-height of the shell, from which 

 point the margin is rounded with considerable regularity to the poste- 

 rior side; from that side the margin is a little more abruptly rounded to 

 the base of the posterior ear, the outer margin of which forms nearly a 

 right angle with the- hinge-margin. Posterior ear small, distinct from 

 the body of the shell, but not separated from it by an auricular furrow. 

 Surface marked by numerous radiating raised lines and costae, which, 

 are irregularly undulating in their direction, the latter being more 

 numerous than the lines, the two diflering from each other only in size. 

 The surface of the anterior ear is faintly marked by numerous fine 

 radiating raised lines, but the surface of the posterior ear is apparently 

 unmarked except by fine lines of growth. Crossing these radiate mark- 

 ings, there are concentric lines and wrinkles of growth. Left valve 

 unknown. 



Height from base to beak, 55 millimeters ; antero-posterior diameter, 

 43 millimeters ; length of hinge-margin, 28 millimeters. 



This species bears considerable resemblance to the one just before 

 described ; but it differs from it in its much greater proportionate height, 

 its almost perpendicular axis, its shorter hinge-margin, smaller posterior 

 ear, and in having the heavier radiating lines or costae more numerous 

 in proportion to the smaller lines. 



Position and locality. — Jura-Trias strata ; locality ISo. 3 of the intro- 

 <luctory portion of this paper, Southeastern Idaho. Collected by Dr. 

 A. C. Peale. 



AvicuLOPECTEN iDAHOENSis, Meek. — Associated with the species 

 last described ; and also from members A and B of the section at local- 

 ity IsTo. 1, a number of examx^les of A. idalioensis were obtained. The 

 type-specimens of this species, as before stated, were obtained at a 

 locality in Lincoln Yalley, about 50 miles northwestward from locality 

 No. 1. Meek's description of it is in Ann. Kep. U. S. Geol. Surv. Terr, for 

 1871, p. 374. 



. This species and the two lierein described as tiew much resemble each 



