LAMELLIBRANCHIATA. 159 



mm. A small specimen is 8 mm. in length, 9 mm. in height, and hinge-line 

 10 mm. 



Formation and localities. In the Marcellus shale at Littleville, Livingston 

 county ; Alden, Erie county, and East Bloomfield, Ontario county, N. Y. 



Leiopteria Conradi. 



PLATE XX, FIGS. 1, i, 4; and PLATE LXXXVUI, FIGS. 1-1. 



Leiopteria Conradi. H.iLL. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 20, fig-s. 1, 2, 4, {5 



in erroi-). Jan., 1883. 



Shell above the medium size, sub-rhomboidal ; body oblique-ovate ; length a 

 little greater than the height ; anterior margin straight, nearly vertical ; 

 iiasal and posterior margins regularly rounded. 



Valves sub-equally convex ; the left valve somewhat more convex than 

 the right. 



Hinge-line straight, longer than the length of the valve, greatly extended 

 posteriorly. 



Beaks acute, directed forward, prominent, situated near the anterior end 

 of the shell. Umbonal region gibbous (in well-preserved shells), moderately 

 convex l^elovv, subtending an acute angle. 



Ear short, separated from the valve by a rounded depression or sulcus, 

 marked l>v a shallcnv, elongate byssal sinus ; extremity rounded. Wing- 

 triangular, nuich extended ; margin concave ; extremity acuminate. 



Test, as indicated by casts or partially exfoliated specimens, marked by 

 fine, closely arranged, concentric lines of growth, which at irregular intervals 

 are crowded and raised into rounded or sub-angular fascicles, giving the 

 surface a decidedly undulated aspect. The strije become more crowded upon 

 the cardinal expansions, especially upon the ear. 



Ligamental area marked by a single longitudinal groove parallel to the 

 hinge-line. 



Two specimens of the left valve have respectively the following dimensions : 

 length 39, and 42 mm., height 32, and 30 mm., hinge-line 42, and 47 mm. 



