14 GENERAL OBSERVATIONS. 



Although I entertain no doubt of the Subcarboniferous age of the fossils 

 from the locality below Ophir City and the one at Ewell's Spring (upper 

 horizon), I am not able to assign them definitely to either of the epochs of 

 that period that are represented by the formations before named in the 

 Mississippi Valley and elsewhere to the eastward of that region. The case 

 is far different, however, with the collection from the Mountain Spring 

 locality, which I refer without hesitation to the Kinderhook group. 



This reference is made in consequence of the identification of no less 

 than five of the species known to exist in rocks of that epoch in the States 

 of the great valley and eastward. The following is a list of those species, 

 together with the localities that furnished either the types or authentic speci- 

 mens : — 



Strophomena rJioniboidalis Wilckins. — Kinderhook group, Burlington, 

 Iowa. 



Spirifer (Martinia) peculiaris Shumard. — Kinderhook group, Missouri 

 and Iowa. 



Spirifer centronata Winchell. — Wavei'ly sandstone, Cuyahoga Falls, 

 Ohio. 



Spirifer {Syringothyris) extemiatm Hall. — Kinderhook group, Iowa and 

 Missouri. 



Terehratula (Dielasnia) Burlingtonensis. — Kinderhook group, Burlington, 

 Iowa. 



Associated with these and other species at Mountain Spring, there is a 

 small Produdus that I have identified with P. parvus Meek and Worthen, 

 the type-specimens of which were obtained from the Chester limestone 

 of Illinois. This might seem to throw some doubt upon the proper identi- 

 fication of the strata at Mountain Spring with the Kinderhook group, were it 

 not for the fact that other species of Productus are known to range through 

 the whole Carboniferous series. Indeed, moi'e species of this genus are 

 known to have this great range than of all other genera of invertebrates put 

 together. 



It is a well-known fact that crinoidal life was eminently characteristic 

 of the Subcarboniferous period ; but, in the Mississippi Valley, it is the Bur- 



