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. 
Fig. 182. 
Orisicania navicella, sp. nov. 
' 7 ? 
Fig. 183. 
Fig. 181. .V cardinal view; showing the hinge-plate and the elevation of the narrow median crest or cardinal pro¬ 
cess. The specimen also retains the teeth of the pedicle-valve and a i>ortion of the dental lamella;, 
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.vtent of the cardinal process. 
Fig 183. A prolile of the same specimen; showing the thickness of the plate and the uncinate form of the cardinal 
process. X 3. (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 
“ Cmtronella, of the type of G. glans-fagea but of great size.” Beecher and Clarke. Notice of a new 
lower Oriskany fauna in Columbia county, New York; Amer. Journal of Science, vol. xliv, p. 414. 1892. 
