appear that the physical conditions favoring the abundant 
production of individuals, has, at the same time, favored 
a degree of variation uzzown under conditions existing 
elsewhere.’ So great is this variation in some of them 
that, in not a few instances, it is at first difficult to recog- 
nize the characteristics of the gasteropods. 
We have found the following species especially abund- 
ant: Platyceras dumosum, P. rarispinum, P. perplexum, 
P. rictum, P. attenuatum, P. contcum. Also Platyostoma 
lineata, P. pleurotoma, P. turbinata, variety FP. cochleata. 
Two other species abundant at this place, but also found 
throughout the entire period, are: /Vleurotomaria lucina 
and Strophostylus varians, 
Gyroceras undulatum, A large cephalopod often meas- 
uring six inches in diameter, is quite abundant in many of 
the layers. It is rolled in one plane, the volutions may be 
in contact or open, and a transverse section is elliptical. 
BRACHIOPODA. 
The Airypa reticularts is a handsome brachiopod found 
sparingly in this period, but more abundant in some of 
the others, especially in the Hamilton. It is well to note 
that the specimens from the Corniferous are larger and 
better preserved than those from some of the other 
periods. It is abundant in the shaly layer at the Indian 
Reservation. 
Strophoinena rhombotdalis is abundant in most of the 
layers. Oftentimes the fossil form is colored red, making 
it very distinct and prominent. 
Strophomena rugosa is usually regarded as a variety of 
the preceding. It differs from it in that it has but eight 
ridges, while the preceding usually has eighteen. 
Orthis eboracensis is a small but very abundant brach- 
iopod, Both valves are usually found together. 
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