LAMELLIBRANCHIATA. 109 



Ligamental area grooved. 



The largest specimen has an entire length of 16 mm., height L0 mm., 

 hinge-line, to the imperfect posterior extremity, 12 mm. A smaller speci- 

 men has an entire length of 14 mm., height 9 nun., hinge-line 15 mm. The 

 smallest specimen measures 10 mm. in length of body and hinge-line, and 

 6 mm. in height. 



*&* 



In form and surface characters this species is quite unlike any other described 

 from these rocks. In some respects it resembles A. eximia, fig. 1, pi. xxv : bul 

 has more extended wing and less elongate body. 



Formation and locality. In the Marcellus shale at Littleville nearWesi Avon. 

 Livingston county, N. Y. 



Actixopteria Doris, n. sp. 



PLATE XVII, FIG. 4. 



Acliruipteria Leander, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 17, fig. 4. Jan., 1883 



Shell small, sub-rhomboidal ; body obliquely sub-ovate; length a little greater 

 than the height ; margins regularly rounded, sloping abruptly from the 

 upper part of the posterior side to the beak. 



Left valve depressed-convex. Right valve unknown. 



Hinge-line straight, about equal to the length of the shell (imperfect in the 

 specimen described). 



Beak depressed, inclined forward, situated at the anterior third of the 

 hinge. Umbonal region not defined, subtending an acute angle. 



Ear not observed. Wing large, flat, not distinctly defined ; margin concave : 

 extremity acute. 



Test thin, marked by regular, equal, rounded radii, with wider flat inter- 

 spaces, and sometimes with obscure intermediate rays. The wing shows 

 finer rays, somewhat crowded at its junction with the body. The fine, con- 

 centric lines of growth are stronger on the anterior of the valve, giving a 

 cancellate aspect to the surface. 



