BRACHIOPODA. 179 



there is danger of confounding it, by the convex pedicle-valve, the distant, 

 elevated, concentric surface-ridges, which have a peculiar undulation as they 

 approach the margins of the foramen. The internal characters of the shell are 

 at once distinctive. (See discussion of these features on page 134.) Length 

 and width of a mature specimen, 50 mm. 



Hamilton group. Leonardsville, Hamilton, Darien and Canandaigua Lake, 

 N. Y. 



SCHIZOCRANIA ScHUCHERTI, Sp. nOV. 

 PLATE IV G, FIGS. 31-33. 



Shell small, usually found unattached ; marginal outline subovate. Surface 

 of pedicle-valve flat or slightly concave; concentrically striated. Pedicle- 

 aperture broad and sharply triangular. Brachial or upper valve strongly 

 convex, often laterally compressed. Umbo full and rotund, incurved at the 

 apex, which is almost, but not quite marginal. Surface covered by numerous 

 simple, sharply elevated, uninterrupted striae, frequently crossed by concen- 

 tric Avrinkles. On the interior of this valve only the strong posterior 

 muscular impressions are distinctly shown. 



Hudson River group. Cincinnati, Ohio. 



ScHizo CRANIA (?) Helderbergia, sp. nov. 



PLATE IV G, FIGS. 31, 35. 



Shell subcircular in outline. Upper valve convex; apex posterior and mar- 

 ginal. Surface covered with fine, closely crowded, elevated, radiating lines, 

 which extend to the apex, and increase by intercalation. Lower valve fiat 

 and of less diameter than the upper. Apex subcentral, posterior. Foramen 

 apparently a narrow triangular slit extending to the margin. A short median 

 septum extends forward from the apex. External surface covered with low, 

 crowded and rather faint concentric lines. On the interior, the surface bears 

 a series of distant, deep but narrow radiating furrows, about twenty-five in 

 number; these do not reach the apex, and increase in number toward the 

 margin. Between them are very fine radiating lines. The animal was para- 



