LAMKU.II:K.\M-III \T\ 



. * ' 



-tilcn* distinct, call-in;,' a flattening of the umUncs and a MUM- in the ventral mar- 

 gin. I'ml.onal ridge premium*, strongly convex. Hinge plate straight, long, 

 thin posterior to the beaks, nincli hi-a\ier in front of them; beneath the beak of the 

 ritflit \.il\e a tooth-like prominence whi.-h tit* into a corresponding depression 

 beneath the beak of the left valve; in front and beneath this depression in the 

 left valve, a strong process pn.j.M-ts obliquely downward, backward and toward the 

 opposite valve, ami i- partly ivceived in a socket that defines the anterior side of 

 the tooth in the right valve, while its lower end curves under that tooth. Muscular 

 scars and pallial line apparently a- in Modiolopsis, excepting that there is a small 

 accessory scar in the hinge plate just behind the anterior udductor.as in Ischyrodonla. 

 Type: <'nli><iii/<i constrirtn n. -\>. 



Kitf. II. <'i'l/iomfa eoH'trictu I'lrich, top nf Tn-nton urmip, Frankfort, Ki'ntii<-k> . a, rljfht vale, 

 .n k ' i h>- iiMiul characters of the speclw: b. Interior of a left valve: r. interior f an nn| rf.. t 

 v.i 



< "Ipomya evidently belongs to the .l/</;W/-///<; with relations to Modiolopsis, Mo~ 

 diolodon and Orthodesma. In none of those genera, however, are the umbonal ridges 

 and the mesial snlci quite such marked features, at any rate it would be rare, so that 

 we may fairly rejr.ird their distinct development in shells of this family as indicative 

 of Colpomi/n. When we come to internal characters all comparisons with the first 

 and la-t of these genera may as well cease, since in both the hinge is practically 

 toothless. In ModioMnn, however, we find cardinal teeth, but every one will admit 

 that they are very different from those of the genus under consideration. Thei 

 nothing to represent the oblique process which projects under the tooth and hinge 

 plate of the right valve, the teeth being approximately equal in the two valves of 



iolodon. 



The i to be placed ino this genus are not numerous and with two possible 



exception- are all new. The exceptions are Modiolopsis milUri Ulrieh. from the 

 I'incinnati rocks, and M. ///></ Hall, said to be a Trenton and Hudson River species. 

 The general expression of these shells is very much as in undoubted species of Col- 

 potnya, but as their hinges are not yet known, their removal from Modiolopsit now 

 would be of very doubtful advantage. Of four new species, C. dtmig&i is a lower 

 Trenton form, while the type of the genus and two other species occur in the 

 upper Trenton of Kentucky. 



