200 NEW YORK STATE MUSEUM 



In O. wool worth anus the shell is so thin as to seldom show these 

 scars. In both valves the plications are sharply defined about the periphery. 

 On the exterior the mutation shows a rather regular inequality in the 

 striae which in total are probably less in number. The differences are 

 sufficient to indicate a modification of the earliest type expressed in O. 

 woolworthanus. 



The shell attains considerable size, fully that of large examples of O. 

 woolworthanus. 



Localities. The best and most abundant specimens are from Shiphead, 

 300 feet below the lighthouse, Cape Gaspe. It has also been found at the 

 Grande Greve outcrops. 



Hipparionyx proximus Vanuxem 



Plate 42, figures 6-11 



Hipparionyx proximus Vanuxem. Geol. N. Y. 3d Dist. 1842. p. 124, 



fig. 29, no. 4 

 Orthis hipparionyx Hall. Palaeontology of New York. 1859. 3:407, 



pi. 89, 90 

 See also Palaeontology of New York, v. 8, pt i, p. 257, pi. 9; and N. Y. State Mus. 



Mem. 3, p. 52 



This characteristic Oriskany species which abounds in the sandstones of 

 central New York but is less frequent in the calcareous facies of Columbia 

 county, occurs at Grande Greve in typical examples. These may not attain 

 as large a size or as ponderous a shell as the species does occasionally in the 

 sandstone of New York but in respect to structures there is no distinction. 

 Some of these specimens replaced throughout by silica show specially well 

 the character of the dorsal valve in which the cardinal area is preserved as 

 short and very narrow, the dental sockets deep and curved, the cardinal proc- 

 ess high, recurved, bifurcate, the posterior grooved faces of the branches 

 standing in the plane of the cardinal area ; the interior is margined by a 

 sharply plicate border which extends all the way around from within the ends 

 of the cardinal line ; the muscular impression of this valve is broadly flabellate, 

 not distinctly divided transversely but separated medially by a low ridge. 

 The ventral valve has the usual large muscle scars with thickened outer edge. 



Specimens measure from 55 to 60 mm in length, by 65 to 70 mm in 

 width. 



Localities. Found rather commonly in association with R h i p i d o- 

 mella musculosa at Dolbel brook near the bottom of the section. 

 Examples of the species are occasionally obtained at Perce Rock. 



Genus RHIPIDOMELLA Oehlert 



The species of this type in the Grande Greve limestones present a very 

 interesting array of characters but it is not easy to interpret their standing 



