BRACHIOPODA. 363 



Dliolulde.] 



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 

 Discinidce than with the Siphonotretidce. 



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 XII6 of Mr. Ulrica's subdivision of the Cincinnati group. The specific name is given in 

 remembrance of the pioneer geologist, John Locke, of Ohio. 



Family DISCINOLE, Gray. 

 Genus ORBIOULOIDEA, d'Orbigny. 



1850. Orbieuloidea, d'ORBiGNY. Prodrome de Paleontologie, vol. i, p. 44. 



1890. Orbieuloidea, HALT,. 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 lamellae 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.) 



