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 Pratten as C. coronata, 

 from the same locality with the preceding species, give from 9 to 12 strise 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. 



Chondes 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 strise (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, ahd at Fultonham 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. 



Clionetes logani, var. aurora. 



Chontttt logani : Norwood and Pratteh, Jour. Acad. Natural 'Sciences, Philadelphia, Vol. iil. 1858. 



(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 foBsil is cited as occurring in the middle portion of the Mountain limestone series; but I have 

 been Informed that this is an erroneous reference, and I have since rtceived specimens, labelled by Dr. 

 HoRWOOD, 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. 



[ Paljiontoloqy IV.] 18 



