New Species of Fossils from Hudson River Group. 31 



other places, and never had any doubt about identifying them, 

 and, recently, have made comparisons with the original spec- 

 imens, with the result of confirming former observations. 



These remarks then, in our estimation, dispose of the 

 three casts figured by Mr. Ulrich. The next point to which 

 we would call attention is the fact that Mr. Ulrich's speci- 

 mens are not by any means as well preserved as the types of 

 Cypricardites hainesi. This is certainly evident from the 

 illustrations, but we can add that the shell of the type of 

 Cypricardites hainesi is the best preserved of any Lamelli- 

 branch shell we have ever seen from the rocks at Richmond, 

 Indiana. We now come to the gist of the subject — the 

 absence of the lateral teeth. On this point we may say, it is 

 well known to all collectors, that they seldom find the teeth 

 of Lamellibranchs in the Lower Silurian rocks well preserved, 

 and in this particular species one of the authors has a hinge 

 line, having the lateral teeth so poorly preserved that they 

 can be distinguished only with difficulty, and we can very 

 well understand from the appearance of the figure of Mr. 

 Ulrich's specimen, that the hinge line is not in a good state 

 of preservation, and that the lateral teeth have been destroyed. 

 Indeed, the improbability that a shell should have such a 

 wide, flat, lateral face and such strong cardinal teeth, and « 

 large posterior muscular scar is so great that we would 

 require that some one should see a well-preserved hinge line 

 before accepting that as the normal condition of the species. 

 After a careful examination of all the specimens in several 

 collections as well as our own, we are left without any doubt 

 on this point. It is for the reasons thus stated that we class 

 Ischyrodonta as a synonym for Cypricardites and Ischyrodonta 

 truncata as a synonym for Cypricardites hainesi. 



Ischyrodonta elongata is founded upon casts that may belong 

 to an undescribed genus. We have a large number of the 

 casts of this species, and some of them appear to be in a 

 better state of preservation than Mr. Ulrich's types. We think 

 the species may be recognized from the casts, while the 

 genus remains in doubt. In its general outline it reminds 

 one of Sphenolinm, but the muscular scars at once separate it 

 from that genus. The muscular scars ^nd wide cardinal line 

 are like Cypricardites, but the high angle of the cardinal line 



