LAMKI.: 



Vanulriulk l 



hue. I'mbo fill I. iiin I tln> u hole surface neatly rounded. < >utlim< obliquely acuminate- 

 uvnid with the anterior IMP! narn>ul\ rounded ami projecting scarcely, if at all, 

 beyond the beak-. from which tin- margin -lope- backward with a gentle curve into 

 U)6 bftB6; posterior end broad. uniformly rounded; cardinal ma: unit 



three-tifths as long as the diagonal length of the -hell. rounding into the interior 

 margin. Surface with faint wrinkle- of growth and probably with finer concentric 

 lines. Shell su! thin. Hinge plate rather narrow, with two long posterior 



and two or three short cardinal teeth in each valve. The latter are difficult to 866 

 becan-e uf tin- clo-.dy iii. -lined Leaks. Anterior ninsciilar impression, as seen in 

 casts of the int. n., |\ visible in a side view, being overhung by the side of 



the Umbo. In an end view they appear like two narrow vertical lobes tapering 

 upward and placed ju-t beneath the free portion of the beaks. Posterior scar very 

 faint, large, ovate, situated a short distance beneath the extremity of the hinge. 

 1'allial line distinct considering the thinness of the shell. 



In the thin shell, its general form, and particularly in the character of the 



anterior mu.-cnlar impres-ion-. I /,//// innl!x reminds strongly of Ambonychin. It i- 



Me that this resemblance i- merely coincidental, but 1 must say that I do not 



l>elieve it, even if I can not now present plausible arguments to show that it 



expree> natural relationship A> a rule, it is not good policy to speculate in 



ontological .[iie-tions, but in the present instance I may be pardoned when I 

 state my conviction that the Ambonychndu are an off-shoot from the same line of 

 development that produced \'<inii.rcmin and the rest of the Cyrtodoniidte. 



Seven of the species of \'.imu-<->ni>i described in this report are found at Minne- 

 apoli- in the same beds that have furnished V. terminalis. All of them occur as 

 casts of the interior, yet not one of the others is at all likely to be confounded with 

 the present species. The principal peculiarities of the latter are the terminal beaks, 

 alrno-t hidden anterior muscle scar.-, the thin shell and the absence of the internal 

 ridge-like thickening which in nearly all species of the genus produces a more or leas 

 well marked sulcu- the umbonal and anterior pa rts of casts. 



Formation .in./ l,,c,ilit,j lini.-st. 1 Cannn Falls, Mlmn*oU. Alo ID 



M**. Rt : :i>0, 8320. 



MIA BATRIA1 



I'l.ATf. XXVVIll IK. -L- .'"\ I' fft. 



Cgrtodonta biyniu,. .IIP. I*.'.' 



/..lyni.miM I 1.1:1. n, !-'- r Minn., p. 340. 



- trian.jui -'- I ''>' M 3- 



Shell of mediu! Mioderately convex, obli-pie. broadly Milwvate 



quadrate, narmwing anteriorly, the hi, i length 'ivoly a- nine is to ten; 



