SP ANTON.] 



AVICULIDJE. 73 



having a very slight backward obliquity; basal outline very profoundly 

 rounded, the deepest or most prominent part being in advance of the 

 middle; posterior margin moderately sinuous below the wing, from the 

 extremity of which it ranges obliquely forward and downward, round- 

 ing regularly into the base below; anterior margin strongly and sub- 

 angularly sinuous under the wing, thence descending with a slight for- 

 ward obliquity and rounding rather abruptly into the base; hinge 

 margin longer than the height of the valve, the anteroposterior diame- 

 ter of which (at any point below) it also decidedly exceeds, ranging 

 nearly at right angles to the vertical axis of the shell ; beaks distinctly 

 convex, rising above the hinge margin, strongly incurved, without ob- 

 liquity, and situated less than one third the length of the hinge margin 

 from the extremity of the anterior wing, which is subtrigonal in form, 

 somewhat convex, a little rounded at the extremity, and very strongly 

 separated from the abrupt shell of the umbo by a deep rounded con- 

 cavity extending from the beak obliquely to the marginal sinus below; 

 posterior wing longer and more compressed, narrower, and more angu- 

 lar than the other; both wings, particularly the posterior one, project- 

 ing decidedly beyond the margin of the valve below. Surface only 

 showing more or less distinct lines of growth. (Right valve unknown.) 



"Height of left valve, 1.50 inches; length of same below the wings, 

 about 1.30 inches; length of hinge-line, 1.90 inches; convexity (of left 

 valve alone), 0.40 inch." 



The types of Pteria (Oxytoma) erecta are small individuals that appar- 

 ently belong to the same species. Dr. White's description is as follows : 



"Shell rather small, appearing to be nearly erect, but the axis is 

 slightly oblique to the hinge-line; both valves convex, but the right 

 one less than the left; hinge-line long, much longer than the axial 

 length of the shell; posterior wing large, its extremity acutely angular 

 and moderately prominent; anterior wing comparatively large, promi- 

 nent, obtusely pointed, defined from the body of the shell by a sinus 

 or furrow in both valves, the direction of which forms a slightly obtuse 

 or nearly right angle with the hinge-line; front, exclusive of the ante- 

 rior wing, nearly perpendicular, the margin forming a nearly regular 

 curve from the front all the way around to the posterior side, where it 

 is flexed with a backward curve to meet the extremity of the hinge- 

 line; umbones somewhat prominent, especially that of the left valve. 

 Surface having a nearly smooth appearance, but the lens reveals the 

 presence of somewhat regularly disposed concentric lines. 



"Length of hinge-line, 32 mm ; axial length of the shell, 2G mm . (Mu- 

 seum.]Sro., 8771.) 



"This shell was formerly referred by me (loc. cit.) to the Avicula lin- 

 guiformis of Shumard, but it differs from that species by having larger 

 wings, a much longer hinge-line, and a much less oblique axis. It may 

 be compared with P. (O.) salinensis White, 1 but it differs in being less 



1 Proc. U. S. Nat. Mus, vol. II, p. 296, PI. 5, Figs. 1 and 2. 



