BRACHIOPODA. 



269 



Billings), of the same fauna, and is carried forward from the Schoharie grit 

 and Corniferous limestone into the succeeding fauna of the Hamilton group 

 (C. impressa and C. Glaucia, Hall). 



All these typical forms of Centronella were preceded in the fauna of the 

 lower Oriskany of eastern New York by a large species, the earliest known 

 possessor of the characteristic naviculoid form and smooth exterior of Centro- 

 nella glans-fagea. The form of the brachidium of this shell (which has not 

 hitherto been described*), has not been determined, but there is every reason 

 to infer that it differs in no essential feature from that of Centronella, for the 

 reason, as already observed, that variation in these shells during the Devonian 

 was virtually restricted to exterior characters and did not affect the conforma- 

 tion of the brachial supports. The hinge-plate of this shell, however, is notably 

 different from that of any of its allies ; it is elongate-triangular, continuous 

 between the crural bases, and bears a median vertical crest, or cardinal process, 

 which begins at the apex, rises rapidly in height, and extends for fully one-half 

 the length of the plate on its upper edge, but at its base is shortened and con- 

 stricted, forming a projecting cardinal spur. 



Fig. 181, 



Fic;. 183. 



Fig. IS'i. 

 Oriskania navicella, sp. nov. 

 Fig. 181. .V cardinal view; showing the hing:e-pl.'xtc .iml the elevation of the narrow median crest or cardinal pro- 

 cess. The specimen also retains tlie teeth of the pedicle-vaUe and a jiortiou of the dental lamellae, 

 though the latter are broken near the surface of the valve. 

 Fig. 182. An enlargement of the hinge-plate; showing the crural lobes and the e.\tent of the cardinal process. 

 Fig 183. A profile of the same specimen; showing the thickness of the plate and the uncinate form of the cardinal 

 process. X .'!, (c.) 



Such an extravagant modification of the normal form of the hinge-plate in 

 Renssel^ria and Centronella is the more remarkable on account of its early 

 age, as this shell antedates the appearance of the typical Devonian species with 

 divided hinge-plate and without cardinal process, and it is proposed to distinguish 



" " Centronella, of the type of C. glans-fagea liut. of great size." Beecher and Clarke. Notice of a new 

 lower Oriskaay fauna in Columbia county, New York; Amer. Journal of Science, vol. xliv, p. 414. 1S92. 



