506 Contributions to Invertebrate Palaeontology. 



hitherto recognized within the limits of the State, and require 

 something- more than a passing notice ; I have therefore made 

 some remarks upon them preceding their descriptions, more ex- 

 tended than would be convenient in this place. 



The species illustrated on Plate XII are from the Huron and 

 Erie Shales with one exception {Aristozoe canadensis) and the 

 remarks preceding their description will sufficiently explain their 

 grouping. 



Those illustrated on the two following Plates, Nos. XIII and 

 XIY, are all from the limestone layers known as the Maxville 

 limestones, and although several are of previously undescribed 

 species, enough. of them are recognized forms to fully establish 

 their geological horizon, which appears to be equivalent to the St. 

 Louis and Chester beds of Illinois and the surrounding States. 

 This conclusion, I believe, had been reached by Mr. F. B. Meek 

 during his work on the Ohio fossils, at least his labels on some 

 specimens of Spirifera contracta in the State Cabinet at Columbus 

 would indicate this conclusion. The possibility of fully and satis- 

 factorily identifying any of the divisions of the Lower Carbonifer- 

 ous formations of the more western States among the beds repre- 

 sented beneath the true Coal Measures of Ohio, must certainly be 

 considered as an advantage in the study of these formations. Xot 

 only is this true from a stratigraphical point of view as enal)ling 

 us to identify a stratum or formation over a much greater extent of 

 country and thereby trace out and locate its history in time; but 

 also palajontologically, as enabling us to satisfactorily identify many 

 of the slightly varying forms of fossils represented in these beds 

 with those from other localities, instead of having them described 

 as distinct species, founded upon minute or imaginary differences 

 resulting principally from a change in the state of preservation or 

 of the conditions of life under which they may have existed during 

 the deposition of the sediments in which they are now found. 

 There seems to be a constantly growing tendency to describe as 

 new species forms which vary in the slightest particular from the 

 established species, and it often arises from the inability to satis- 

 factorily identify the beds in which they arc^ found with those from 

 other localities wiiere the stratigraphical relations are already known, 

 and I cannot but regret that it is not practicable to work out the 

 fossils of other of the Ohio formations, as I am fully persuaded there 

 are several of these which could be positively identified with well- 



