126 
PALEONTOLOGY OF NEW YORK. 
pedicle-groove may then be regarded as the track left by the advance of the ex¬ 
ternal opening of the foramen, closed by later testaceous secretions and quite 
homologous to the anterior portion of the great depression surrounding the pedicle- 
slit in Discinisca. In certain thick-shelled species, like Orbiculoidea conica and O. 
Forbesi (to which reference will again be made under the discussion of the genus 
Schizotreta, Kutorga), the evidence of the external furrow ends abruptly with 
the disappearance of the pedicle-groove into the substance of the valve. In 
general, however, the shell of palasozoic “ Discinas ” is very tenuous, and their 
compression in the process of fossilization often confounds the features of the 
inner and outer • surfaces of the pedicle-area, making them appear continuous. 
It seems evident that in these fossils the groove upon the external surface is, 
as a rule, of essentially the same character as that seen in Davidson’s figures 
of Orbiculoidea Forbesi * Dwight’s figures of 0 . conicaf and those of the latter 
species given on Plate IY f of this volume ; outside the foramen the concentric 
lines following without interruption, as on any other portion of the external 
surface. 
On the internal surface of the pedicle-valve the track of the pedicle-groove 
extends along nearly the entire radius of the shell. In no species have we 
found the internal character of this feature so well retained, and showing so 
clearly the changes passed through from youth to maturity as in an undescribed 
species,^ from the Cuyahoga shales at Berea, Ohio, and in D. nitida from the 
shales of the lower Coal Measures, at Springfield, Illinois. The specimens 
from these formations frequently preserve the test without mutilation or much 
distortion. Early in the life of these species the foramen has penetrated the 
internal surface near the apex, and whatever groove has been made upon the 
outer surface by the radial progress of the foraminal aperture is also marked on 
the inner side, and is usually somewhat calloused, conspicuously so in adult 
* Silurian Brachiopoda, pi. xii, figs. 14, 14 b, 15, 18. 
t American Journal of Science, 1880, pi. xxi, figs. 1-5. 
t This species has come to us from various quarters labelled “ Discina Neiuberryi, Hall.” With the 
latter however it does not agree, the pedicle-area not being elevated nor so broad as in that species, and 
the brachial valve rather more convex with its apex nearer the center. The original specimens of D. New- 
berryi are from a ferruginous sandstone, 110 feet below the conglomerate at Cuyahoga Falls ; those of the 
species in question, which may be termed Orbiculoidea Hwzeri, from greenish-black shales at Berea, Ohio. 
