Bn aat BRACHIOPODA. 363 
This species is readily separated from all other American species now referred 
to the genus by its thin valves, and particularly by the absence of all spines and 
imbricating growth lines on the posterior two-thirds of the dorsal valve. This 
species may prove to be the type of a new genus with relations nearer to the 
Discinide than with the Siphonotretide. 
Formation and locality. —Two specimens have been procured, one of which, showing more of the 
detail, was recently collected by Mr. F. W. Sardeson on top of the hill just north of the Cincinnati Uni- 
versity, in beds XIIb of Mr. Ulrich’s subdivision of the Cincinnati group. The specific name is given in 
remembrance of the pioneer geologist, John Locke, of Ohio. 
Family DISCINIDA, Gray. 
Genus ORBICULOIDEA, d’Orbigny. 
1850. Orbiculoidea, d’ORBIGNY. Prodrome de Paleontologie, vol. i, p. 44. 
1890. Orbiculoidea, HALL. Paleontology of New York, extract vol. viii, pt. i, p. 129. 
Description: “Shells subcircular or subelliptical in outline, inequivalve. Apices 
eccentric. Pedicle-valve depressed convex, or flattened, with the apex slightly ele- 
vated and inclined posteriorly. On the exterior of the valve a narrow pedicle-furrow, 
abruptly intercepting the ornamentation, but not penetrating the substance of 
the shell, begins just below and behind the apex, extends over a greater or less 
portion of the radius of the valve, and, at its distal end, is produced into a short 
tubular sipho, which traverses the substance of the shell obliquely backward, 
emerging on the interior surface, where it produces a narrow groove, and usually 
terminates before reaching the margin of the valve. On the interior, the position 
of the external groove is marked by a thickened ridge extending from the apex, and 
this is continuous with the thickened margins of the internal groove, which, in 
advanced age, may become so developed as to envelop this groove, except at its 
outer end. 
“The larger or brachial valve is depressed-conical, with the apex more strongly 
directed backward than in the opposite valve. The interior shows a fine longitudinal 
ridge or septum extending from the apex forward. Otherwise the internal markings 
are not satisfactorily known. 
“Shell-substance composed of alternating lamelle of corneous and mineral 
matter, the latter often removed in fossilization, making the shell appear essen- 
tially phosphatic. Surface ornamentation usually consisting of fine, crowded or 
distant, sometimes lamellose concentric lines, occasionally crossed by radiating 
lines or ridges. 
“Type: Orbicula morrisi Davidson.” (Hall, op. cit.) 
