602 THE PALEONTOLOGY OF MINNESOTA. 
[Ctenodonta alta. 
two sharply defined muscular scars and pallial line in each valve.* Hinge plate 
rather narrow, the teeth numerous, over thirty, as usual very small centrally, grow- 
ing larger gradually towards the ends of the hinge. 
This species is distinguished from C. astartiformis Salter, by its larger size, greater 
width, more erect form, and comparatively coarse and regular concentric lines. C. 
compressa is not 80 convex, especially in the umbonal region, has more pointed beaks 
and much finer strie. 
Formation and locality—Not uncommon in the middle division of the Galena at Wykoff and other 
localities in Fillmore county, Minnesota. 
Crenoponta ALTA Hall. 
PLATE XLII, FIGS. 93 and 94. 
Tellinomya alta HALL, 1861. Rep. Supt. Geol. Sur. Wis., p. 27; MEEK and WORTHEN, 1868, Geol. 
Sur. Ill., vol. iii, p. 309. 
Shell (internal cast) small, rather strongly convex, nearly erect, subtriangular, 
the length, hight and convexity, respectively, about 11.2, 11.5 and 6.3 mm.; base 
broadly rounded, semielliptical; beaks elevated, nearly central, arching slightly back- 
ward; anterior and posterior sides nearly equal, sloping abruptly from the beaks at 
an angle of about 85°, the anterior dorsal outlines very gently convex, the posterior 
correspondingly concave; beneath the ends of the hinge the outline on both sides 
curves rapidly into the base. Muscular scars large and comparatively distinct, the 
posterior one nearly rounded, the other more oval; the anterior one lies in the wider 
lower end of a shallow sulcus which may be traced almost to the beaks. The hinge, 
Prof. Hall says, is marked by from twenty to twenty-five very small curved teeth on 
the anterior (posterior) side and from ten to fifteen on the posterior (anterior) side. 
This rare species is a little smaller, not quite as high, more erect and less convex 
in the basal outline than C. intermedia. In the latter, as well as in all the other 
species of this section of the genus, save C. recurva, the anterior half of the outline 
is more uniformly rounded. 
Formation and locality—The specimen described by Meek and Worthen came from the Galena 
near Mount Carroll, Illinois, while Hall’s original type is from, presumably, an equivalent horizon at 
Dodgeville, Wisconsin. The specimen here used, which is precisely like the Illinois example, is from 
the shaly lower beds of the Galena near Fountain, Minnesota. 
*In the original description it is stated that a small pair of scars is situated above the posterior adductor impres- 
sions. This statement I now believe rests upon faulty observation. 
