52 NEW YOEK STATE MUSEUM 



are visible in the interspaces but seldom cross the radial striae. Con- 

 centric varices of growth are also frequent, specially near the margins. 



The cardinal area of the pedicle-valve is triangular, broad and 

 erect, seldom showing distortion. In but a single instance has attach- 

 ment been observed and that is the young shell figured on plate 7, 

 which adheres by its entire outer surface to a valve of Meristella 

 and is associated with Autodetus, Hederella and some other 

 parasitic growths. The deltidium is pronounced. On the interior the 

 markings are those characteristic of the^ genus ; the brachial valve 

 bears an erect, continuous cardinal process, divided into two lobes, 

 each grooved on its outer face. The lateral walls of this process are 

 continued inward to form the strong dental sockets. 



This very common species has no close ally in the Devonic faunas 

 of the neighboring region. The Orth. woolworthana and 

 Orth. deformis of the Helderbergian are large shells with a much 

 finer surface striation, and perhaps the nearest approach is found in 

 the Orth. arctostriata of the Hamilton shales, from which a 

 difference will be found in outline and character of surface. Most 

 closely allied also to O. becraffcensis is an undescribed species in 

 the Gaspe sandstone. 



Hipparionyx proximus Vanuxem 



1842. Hipparionyx proximus Vanuxem, Geology of New York; repH on third 

 dist. p. 124, fig. 29, no. 4 



1892. Hipparionyx proximus Clarke, op. cit. p. 413 



The specimens of this well known Oriskany species which have 

 been obtained are of large size and characteristic in all details. 



Stropheodonta lincklaeni Hall 



Plate 7, flg. 37 



1859. Strophodonta lincklaeni Hall, Paleontology of New York. 3 : 415, 

 pi. 93, fig. 2,3 



1892. Stropheodonta lincklaeni Clarke, op. cit. p. 413 

 This species was not originally very clearly defined on account of 

 the imperfection of the material, but the name has been generally 

 applied to plane or slightly convexo-concave stropheodontids with a very 



