666 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



which is relatively short and blunt and carinated on the outer, more 

 convex side — by its more slender form and absence of the carina. The 

 latter is very common in a highly fossiliferous member of the Yellville 

 formation at Smithville, Arkansas. The curved variety of C. Iceithi 

 is found also at several localities in Christian County, Missouri, and at 

 other points farther east in that State to Lutesville. Finally, I have 

 it from the Cumberland and Lehigh valleys in Pennsylvania. In all 

 cases this and the other species of Ceratopea occur in limestones and 

 dolomites which had been determined as Canadian before the strati- 

 graphic significance of these fossil opercula had been ascertained. 



Canadian limestones in central and western Texas. — The Cambrian sec- 

 tion in central and western Texas is in all respects the same as in Okla- 

 homa. In both States there is a basal sandstone, followed by a limy and 

 shaly zone well speckled with glauconite and a more calcareous zone — 

 the Honey Creek member — above that. These three zones constitute 

 the upper Cmbrian Reagan or Katemcy formation. Above this come 

 beds corresponding to the basal division of the Arbuckle limestone. This 

 consists of thin-bedded pure limestone and more massive dolomite and 

 marble, and is essentially the same in central and possibly also in west- 

 ern Texas as in Oklahoma. The last may be of Ozarkian age, but it is 

 thought more likely that it will prove to be late upper Cambrian. This 

 finally is succeeded by more or less cherty Canadian limestone. 



The Canadian part of the section in central Texas was not carefully 

 discriminated from the underlying dolomites and limestones. It may be 

 wanting locally. In other places it is less than 100 feet, while its maxi- 

 mum thickness in San Saba, Llano, and Burnet counties seems not to 

 exceed 300 or 400 feet. At that it covers considerable areas in these 

 counties, providing, as is believed to be the case, all the cherty Eopaleo- 

 zoic limestones are of this period. It is succeeded by either early Penn- 

 sylvanian limestone or Cretaceous deposits. 



The fauna of these Canadian beds has been collected at only two or 

 three points, and even at these no determined effort was made to pro- 

 cure it. Perhaps fossils are rare and unequally distributed, but where 

 noted the chert and limestone was filled with organic remains. The 

 species so far collected — about 15 in number — are in every case also 

 represented in the particular facies of the Yellville fauna found at 

 Lutesville, Missouri. At both localities the commonest fossils are Cera- 

 topea Iceithi (curved variety), Bathyurus amplimarginatus , and the 

 HeJiocotoma? usually associated with the first. 



Judging from excellent collections of fossils in the National Museum, 



