SCAMMON : THE UNIONID^ OF KANSAS, PART I. 349 



it belongs have marked peculiarities of shell. The nodules 

 vary much in different specimens, and I have seen specimens 

 in which they were low and evenly rounded, but generally 

 this is the most striking character of the shell. The epider- 

 mal markings and the pseudocardinals exhibit minor varia- 

 tions. 



Quadrula metanevra Rafinesque. Plate LXXXI, fig. 1. 



Obliquaria (Quadrula) metanevra Rafinesque, Ann. Gen. Sci. Brux., 

 V, 1820, p. 305, pi. Lxxxv, figs. 15, 16. 



Shell generally of moderate size, thick, thickest anteriorly, 

 somewhat compressed, trapezoidal in outline. Anterior mar- 

 gin and the anterior half of the ventral margin almost form- 

 ing a semicircle, remainder of the ventral margin at first 

 slightly incurved and then forming a rounded and produced 

 lobe, of which the ventral portion of the posterior margin 

 forms the upper part. Upper portion of posterior margin 

 almost straight ; dorsal margin straight or slightly curved. 

 Umboidal ratio, approximately one-third. Umbones large 

 and full ; when not worn (as is usually the case) , triangular 

 and sharp. Anterior and lateral umboidal slopes fully 

 rounded, and more or less ornamented with large, low, tuber- 

 cles, sometimes entirely smooth ; umboidal ridge very promi- 

 nent, rounded abruptly anteriorly and posteriorly, widening 

 ventrally, generally bearing several large irregular nodules 

 and also low tubercles ; posterior slope rounded and orna- 

 mented dorsally with obscure broken ridges. Lines of growth 

 prominent, regular, and continuous. Epidermis variable in 

 color, from straw to deep chestnut-brown, often marked 

 with dark green triangular patches, the apices of which are 

 directed vertically. Ligament short, thick, honey-brown to 

 black in color. 



Interior : Pseudocardinals large, low, massive, coarsely 

 striate, double in the left valve, with one large and one or 

 two low auxiliary teeth in the right valve. Laterals short, 

 very heavy, generally curved, but sometimes straight oblique, 

 sometimes inclined to be double in the right as well as the left 

 valve. Interdentum broad and flat. Anterior adductor cica- 

 trix well marked but shallow, placed in front of the pseudo- 



