20 PALAEONTOLOGY OF NEW JERSEY. 



in contradiction of this statement that the oysters, for instance, which by 

 many are classed as the most lowly organized of the entire group, do not 

 appear at all in the Palaeozoic formations.^ But this may prove to be a 

 retrograde from a higher type, and not invalidate to any very great extent 

 the statement above made. In arranging and classifying the fossil moUusca 

 with other forms of animal life in a palseontological collection I find it most 

 convenient and instructive to classify them in this way; and I also find 

 that it leaves a by far less number of breaks and gaps in the chain of suc- 

 cession than when the arrangement is made in the opposite direction. Had 

 it not been for this circumstance I should have arranged them after the 

 other method, had it been for no other reason than that I should prefer to 

 conform to that generally accepted by other writers if it were possible 

 without conflicting with nature's own arrangement. 



In the adoption of generic divisions among the very imperfect material 

 for generic distinction with which I have had to work, I have been gov- 

 erned by reasons which have forced themselves upon my mind as I have 

 progressed with the work. When I first commenced to study and classify 

 the forms under consideration, I was much inclined to throw aside most of 

 the more recently proposed generic divisions founded by Mr. T. A. Conrad 

 upon such poor material, and often upon a single imperfect cast of a single 

 valve. But I have found that in many instances, where among later col- 

 lections than those he at first used, the shells themselves were found pre- 

 served, they show strong generic differences, and afford in most instances 

 fully as good grounds for separation as those usually adopted among 

 recent shells; consequently I have been compelled, almost against my own 

 will, to accept his divisions. While in other cases I have found it totally 

 impossible to establish any refutation of their value; so that in the end I 

 have concluded to adopt the generic divisions nearly as proposed by him, 

 offering only a few criticisms by the way. This, I think, will perhaps prove 

 in the end the most satisfactory manner of dealing with the very imperfect 



1 There is only one species of true oyster, so far as I know, described from the Palaeozoic rocks. 

 This one, Ostrea patercula, Winch., described as coming from the Waverly sandstones at Burlington, Iowa, 

 I had the privilege of seeing some years ago^ and I am perfectly confident that it is a young specimen 

 from the yellow limestone sands of the Middle Marl Beds of the Cretaceous of New Jersey, which had 

 gotten by some means mixed among the Waverly group fossils by accident. 



