CHONETES OF THE HAMILTON GROUP. 
137 
the same space; and C. martini, 12 and 13 in the middle and 9 on the front. 
Specimens which were recognized by Messrs. Norwood and Prat-ten as C. coronata, 
from the same locality with the preceding species, give from 9 to 12 striae in the' 
space of two-tenths of an inch; in four specimens, the number 9 occurring four 
times, 10 four times,, 11 twice and 12 once. 
Chonetes syrtalis of Conrad gives from 8 to 15 striae in the same space, one 
large individual (figured on Plate 22) giving 6 in front, 8 in the middle and 9 at the 
side. The smallest specimen measured, gave 14, 15 and 16, while the larger.ones 
gave fewer striae (8 - 12) in the same space. These measurements, if of any value 
at all, serve to confirm the view that all these varieties are but a single species. 
Geological formation and localities. This species in its typical forms, occurs in 
the calcareous shales of the Hamilton group on the shores of Cayuga, Seneca and 
Canandaigua lakes ; at Moscow and York, Livingston county; at Darien and 
Eighteen-mile creek, Erie county, and at other localities. In the form denominated 
C. syrtalis , it occurs in the harder shales at Cazenovia and Hamilton in Madison 
county, in Otsego county at several places, and at Pultonham and Summit in 
Schoharie county. It occurs in large numbers, associated with other known fossils 
of the Hamilton group, at the Bake-oven on the Mississippi river in Illinois. 
CSiouetes logani, var. aurora. 
Chonetes logani : Norwood and Pratten, Jour. Acad. Natural Sciences, Philadelphia, Vol. iii. 1855. 
(Memoir, pa. 30, pi. ii, f. 12, a, b, c.) 
The following description is given as above: 
“ Shell small, transverse ; having its greatest breadth near the cardinal 
“ border. Dorsal valve inflated; without a sinus; covered with about 
“ thirty rugose ribs. Ears small and scarcely separated from the dorsal 
“ vault ; beak rather large and recurved. Ribs flattened and crossed 
“ by fine lines : many of them are dichotomous. Area and ventral 
“ valve unknown. Traces of tubes can be seen on the cardinal edge, 
“ but the number cannot be ascertained. Dimensions : length, 6 milli- 
“ metres; breadth, 9.”* 
* The fossil is cited as occurring in the middle portion of the Mountain limestone series; hut I have 
been informed that this, is an erroneous reference, and I have since received specimens, labelled by Dr. 
Norwood, from the Oolitic beds of Burlington, Iowa. The species is probably limited in its upward range 
to the lower calcareous beds of Burlington, and to the same horizon in the Mississippi valley. I have given 
a very different: species under this name in the Iowa Geological Report, having accepted labelled specimens 
as authentic,, without relying on the description and figure, cited. 
[ Paleontology IV.] • 18 
