484 THE PALEONTOLOGY OF MINNESOTA. 
(Classification 
valve beneath the beaks, in Matheria there are two in the left and one in the right, in 
Cypricardites three or more, and these are added to by the development of lateral 
teeth (fig. 36, [V); some types may have radiating teeth (fig. 36, I and II); in others 
the whole hinge margin will be divided transversely into numerous small teeth, while 
still others may present a combination of short transverse and long lateral teeth. On 
the whole, after giving due consideration to other pecularities, modifications in the 
structure of the hinge are to be ranked as of the highest importance. 
CLASSIFICATION. Z 
The class Lamellibrachiata, or Pelecypoda, is variously divided by authorities. 
It is neither necessary nor desirable that the numerous systems should be considered 
here, since it is my impression, and here I merely follow the opinions of some of our 
latest and highest authorities, that they are all more or less misleading and inade- 
quate. The fact is, we have not yet arrived at that stage in knowledge where a 
really natural classification is possible. Too little of the paleozoic representatives 
of the class is known well, and until more is learned of the evolution of the recent 
types from their fossil ancestors no attempt is likely to prove more than provisional. 
What we want now are facts and when sufficient of them have accumulated I doubt 
not the desired natural scheme of classification will evolve itself. 
Still, since we have systems, they may as well be used till something better is 
furnished. Of course, only paleozoic types are here considered, and in viewing these 
alone, I cannot say that I am satisfied with the following arrangement. In drawing 
it up I have paid due attention to the arrangements proposed by Tryon, Stoliczka, 
Zittel, S. A. Miller and others, and sought to avoid what has seemed objectionable in 
each. At best the result is premature, and in submitting it in the hope that it may 
prove a little nearer the truth than their schemes, I beg that it may be considered 
with lenity. 
