FOSSILS OF THE DEVONIAN. 



119 



Strcphomena (Strophodonta) demissa Hall, 1857. Tenth Ann. Eep. N. Y. State Cab. Nat. 



Hist,, p. 137. 



Strophodonta demissa Hall, 1858. Geol. Iowa, vol. i, pt. 2, p. 495, pi. iii, fig. 5. 

 Strophomena demissa Billings, 18C1. Canadian Jour., vol. vi, p. 341, figs. 116-118. 



demissa Billings, 1863. Geology of Canada, p. 367, figs. 377 a-d. 

 Strophodonta demissa Hall, 1867. Pal. N. Y., vol. iv, pp. 81, 101, and 114, pis. xi, xii, 



xvii, xix. 

 Sti'ophomena (Strophodonta) demissa Meek, 1868. Trans. Chicago Acad. Sci., vol. i, p. 87, 



figs. Qc-c. 

 Strophodonta demissa Nicholson, 1873. Pal. Prov. Ontario, p. 65. 



demissa Whitfield, 1883. Geol. of Wisconsin, vol. iv, p. 327, pi. xxv, fig. 18. 



This species in New York occurs throughout the Devonian. It has 

 also been found in Illinois, Iowa, and to the far Northwest, in the Mackenzie 

 River Basin In the Eureka District it is restricted, as far as known, to 

 the Lower Devonian horizon. The specimens are below the average size 

 of those from the Hamilton Group of New York, corresponding in this 

 respect to the Upper Helderberg form; they are also more finely striated. 



Formation and localities. Lower horizon of the Devonian limestone, 

 midway of Gray's Canon, Eureka District, and at Lone Mountain, 18 

 miles northwest of Eureka, Nevada. 



Strophomena (Strophodonta) patersoni Hall, 1857. Tenth Ann. Eep. N. Y. State Cab. 



Nat, Hist., p. 114. 



Strophomena Patersoni 9 Billings, 1861. Can. Jour., vol. vi, p. 340, fig. 115. 

 Strophodonta patersoni Hall, 1867. Pal. N. Y., vol. iv, p. 89, pis. xii, xiii. 

 Strophomena Patersoni Nicholson, 1873. Pal. Prov. Ontario, p. 67. 



There is but one specimen of the ventral valve of this species in the 

 collection, but its depressed convex form, arching wrinkles between the 

 coarser stria?, and the fine intermediate radiating striae give it all the promi- 

 nent characters of the species. In New York and Canada, S. Patersoni is 

 an Upper Helderberg species, not being known in the Hamilton or Chemung 

 Groups. Its horizon in New York and Canada is the equivalent .of the 

 Lower Devonian horizon in the Eureka District. 



Formation and locality. Devonian formation, lower horizon, Lone 

 Mountain, 18 miles northwest of Eureka, Nevada. 



