Gkabau — Faunas of the Hamilton Group. 



327 



IV. COMPARISON OF THE FAUNAS OF THE HAMILTON 

 GROUP AT EIGHTEEN-MILE CREEK WITH THE 

 RECORDED FAUNAS OF THAT GROUP AT OTHER 

 LOCALITIES. 



In 1888, Professor Samuel Calvin* described the vertical range of cer- 

 tain species of fossils of the Hamilton period, in the region about Widder 

 (Thedford), Arkona, and Bartletts Mills, Ontario, one hundred and thirty 

 miles west of Eighteen-mile creek. In a section two hundred or two 

 hundred and fifty feet thick he made three distinct subdivisions, based on 

 palaeontologic evidence. The lower division exposed below Bartletts Mills 

 and near Arkona is characterized by the predominance of Spirifer mucronatus, 

 Conrad, of the ordinary extended form with comparatively flat valves and 

 many plications. This is essentially the form which I have noted in the 

 foregoing pages as characteristic of the Lower Shales of the Eighteen-mile 

 creek region, or the type form of my Spirifet' mucronatus fauna. Associated 

 with this species, on the Ontario Hamilton is Chonetes lineatus, Conr. which 

 in the beds about Eighteen-mile creek is represented by C. scitula. Phacops 

 rana occurs in both. 



In their principal species the beds agree at the two localities, and may be 

 regarded as equivalent. 



The third division, namely, that exposed at Widder, is characterized by 

 the thick short form of 8. rmicronatus with few plications, well known as 

 characteristic of that locality. I have before me a number of the Widder 

 specimens, and on comparing them with specimens of S. consobrinus from 

 Eighteen-mile creek, I can find few points of diri'erence in the external charac- 

 ters. The most important difference is the greater height and more arcuate 

 character of the hinge area of 8. consobi'inns, and the somewhat greater regu- 

 larity and prominence of its zigzag striae. But it might be questioned 

 whether these differences are not such as would come from development of 

 the same species in widely separated localities. 



The following species are recorded as associated with this 8. mueronatus 

 at Widder : 



Cyrtia (=Cyrtina) Hamiltonensis. 

 Athyris spiriferoides (small form). 

 (?) Liorhynchus multicostus. 



* Am. Geol. Vol. I, p. 81, et seq. 



