604 THE PALEONTOLOGY OF MINNESOTA. 
[Ctenodonta similis. 
Crenoponta simiiis Ulrich. 
PLATE XLII, FIGS. 102—106. 
Tellinomya similis ULRICH, March Bs) 1892. Nineteenth Ann. Rep. Geol. and Nat. IES Sur. Minn., 
Tellinomya (Nucula) lepida yenees April 9, 1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 339. 
Shell small to medium size, moderately ventricose, subtriangular, the length 
and hight respectively as five or five and a half is to six. Umbones full, rounded, 
the rostral portion rather strongly recurved, with the beaks small and projecting 
slightly above the hinge. Antero-dorsal edge convex, thick, flattened, but not 
sharply defined. Postero-dorsal edge rather strongly concave, impressed so as to 
form an illy-defined imperfect lunette. Anterior outline almost uniformly convex, 
curving neatly into the well rounded ventral margin; posterior side rather narrowly 
rounded. Surface of valves almost uniformly convex, highest a little above the 
center, generally with a few well marked varices of growth and with finer concentric 
lines in the lower part. Hinge plate of moderate strength, with numerous small 
teeth (thity-five to forty-two); in the largest examples seen with about twenty-seven 
anterior and fifteen posterior to the beak; posterior teeth the largest. Muscular 
scars moderately impressed, always distinguishable. 
The shape of this shell is exceedingly like that of C. astartiformis Salter, though 
as a rule proportionally a little longer and scarcely so ventricose. The posterior 
lunette also is somewhat deeper, but the principal differences le in the hinge. The 
hinge plate, namely, in Salter’s species, is somewhat stronger, while the denticles 
are more bent, larger and less numerous. The teeth, furthermore, are largest on the 
anterior side, while in C. similis the opposite is the case. It is also very much like 
the associated C. recurva, but is distinguished by being a little higher, more uniformly 
rounded on the anterior side and without the anterior sulcus. More important dif- 
ferences are the greater tumidity of the umbones, less prominent beaks, less strongly 
defined anterior and posterior lunettes and weaker hinge plate. Casts of the interior 
are separated chiefly by the greater thickness of the rostral portion. They are also 
nearly always of smaller size than those of C. recurva. 
Formation and locality.—Upper beds of the Hudson River group, Spring Valley and other parts 
in Fillmore county, Minnesota, and at Blanchester, Ohio. 
CrmnoponTa oBLigua Hall. 
PLATE XLII. FIGS. 8&3—87, 
Nucula obliqua HALL, 1845. Amer. Jour. Sci. and Arts, vol. xliii, p. 292. 
Tellinomya ? obliqua Mek, 1873. Pal. Ohio, vol. i, p. 139. 
Paleoconcha obliqua and P. faberi MILLER, 1889. North Amer. Geol. and Pal., p. 498. 
Shell very small, broadly acuminate-subovate; or, without the triangular rostrum, 
