LAMKl.UHi: AM MIA 



loot* (UbrlU. 



flu- part that i- in front of the beaks. Several spent'- <>f l'./m<r. M'./ present a sin, 

 exteniiil appearance, l.ut they have all a thicker shell an. I an- .|iiit<> dillerent intern- 

 ally, >) that casts of the interior could not possibly l>e confounded. 



l-.-n-tli. ll.-J iniii.: from umbone to postero-basal margin. U.s mm.: bight at 

 middle of -hell. 1:1 mm. thickne. 11 mm. 



'i/ify. Due of Hi- mlddl.- Catena, about thirteen mile* M>utb of Cannon KalU, 



CTRTODOMTA OLA BELLA LYnV/,. 



1'I.ATK \\\l\ I IOS. J7od .. 



~\cardit* gla> 1888, NIoeUM-ntli Ann. Rp. Ocol. and Nat. Hlat. Sur. Minn., 



rM. 

 Ctprifantitet minnr*>frnj SAKDK8ON, April, 1892. Bull. Minn. Acad. Nat Scl., vol. III. p. 338. 



Shell of medium -i/e. moderately convex; broad ovate or subquadrangular in 

 outline, with the back straight an<l rather long, the posterior margin broadly rounded. 

 -ometimes nearly vertical and slightly straightened in the middle, above making 

 an <.l.t usely angular or more or less rounded junction with the hinge line; ventral 

 a i i-l anterior margins rounded, the latter turning rather sharply backward at the 

 hinge. Beak- situated well forward, small, very slightly prominent, the umbonal 



>n full, with the line of greatest convexity not sufficiently defined to be called 

 a ridge extending obliquely across the valve from the beak linal -lope Hat, 



rather al>rupt; between this and the undefined umbonal ridge, the surface is again 

 tlatteiifl: anterior and basal slopes gently convex. Surface marked with somewhat 

 irregular concentric lines of growth. 



Good moulds of the interior show that the hinge plate was strong, the liga- 

 mental area very narrow, the cardinal teeth at least two and strong, and the poster- 

 ior teeth two or three in each valve. The beaks are prominent, incurved, and com- 



-ed because of a sulcus that crosses the valves a little obliquely, but is lost before 



reaching one-half the distance to the ventral border. On each side of the sulcu- i- a 



faint ridge. Anterior adductor distinct, rather small, ovate, acuminate below. 



1'allialline distinct, especially the anterior part where it appears as a sharply 



letint-.l pu-tulo-e ri'lge in the cast. Posterior adductor ovate, the long diameter 



:<-al. nearly three time- the size of the anterior, situated ahout one-third of it.- 



length beneath the posterior end of the hinge plate. 



Thi> tine shell is an early form of the group of species of which C. germ 



'lillinysi are more typical representatives. It is di.-tiiij/uished 

 from them all l>\ the more anterior position of the beaks, and great- r promin. 

 of the antero-basal margin. The next species, though very similar in most respects, 

 belongs to another group of species, in which the internal r id stilru- i- 



indistinguishable. 



