Grabau — Faunas of the Hamilton Group. 



241 



II. THE VERTICAL DISTRIBUTION OF THE INVERTEBRATE 

 FOSSILS IN THE HAMILTON GROUP OF EIGHTEEN-MILE 

 CREEK AND ADJACENT TERRITORY. 



CRUSTACEA. 



TRILOBITA. 



Genus Phacops, Emmrick. 



1. Phacops raxa, Green. 



1888, J. Hall and J. M. Clarke, Pal. N. Y., vol. 7, p, 19, pi. 7, 8, 8a.* 



This is the most widely distributed and characteristic fossil in the Ham- 

 ilton group of this region. It occurs throughout the mass, and usually is 

 abundantly represented. I have found it in the lowest beds of the group on 

 the lake shore, as well as in the transition beds and in the upper Marcellus 

 shales. In these last mentioned beds it is, however, not very abundant. It 

 is the characteristic fossil of the Trilobite beds occurring in them almost to 

 the exclusion of every other fossil, but is mainly represented by cephala and 

 pygidia. In the overlying beds this species is by no means as abundant as in 

 the Trilobite beds, but it nevertheless is an important constituent of the fauna. 

 In the Encrinal limestone it is a common form, and although the specimens are 

 usually poorly preserved, they indicate by their size, that the species lived 

 under favorable conditions. Two specimens measured, gave 40 and 50 mm., 

 respectively for the greatest width of the cephalon. In the Moscow shales 

 the size decreases somewhat but the individuals are abundant. Specimens 

 have been found up to within a foot or eighteen inches of the Styliolina 

 limestone. 



Genus Cryphaeus, Green. 



2. Cryph.eus Boothi, Green. 



1888, J. Hall and J. M. Clarke, Pal. N. Y., vol. 7, p. 42, pi. 16, 16a. 



This species is usually associated in the Trilobite beds with the preceding, 

 but is far less common. It is likewise mainly represented by cephala and 

 pygidia. It is common, and occasionally abundant in various parts of the 



•As the bibliography of each species is given in the work cited, no attempt has been made to repeat it here. 



