FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 39 



Orthis goodwini. N - SP - 



Plate XVII., figures 30, 31 and 32. 



Shell small, sub-circular or sub-quadrate ; moderately convex in both valves ; 

 hinge-line short, equal or less than half width of shell ; cardinal extremities 

 rounded ; lateral margins almost straight, or very slightly curved; they diverge 

 towards base, in consequence of which greatest width of the shell is close to 

 base or front; the basal margin is broadly curved, with its central portion 

 either straight or slightly inflected. 



Ventral valve is somewhat more convex in its umbonal region than dorsal, 

 but in its basal half it is the reverse. Its greatest convexity is just below 

 umbo, from where it slopes in a very gentle curve to lateral and basal margins, 

 but more rapidly, even almost abruptly, to the cardinal lines ; umbo moderate, 

 beak a little elevated above opposite valve, sharp- pointed and slightly arched, 

 but not incurved. Cardinal area short, but comparatively high, limited by 

 sharp margins, and divided by an open, triangular foramen, which is partly 

 closed at its base by the cardinal process of the dorsal valve. 



Dorsal valve moderately convex ; point of greatest convexity a little above 

 middle of valve, from where it slopes in a gentle curve to all the margins and 

 to the beak, giving the valve over its whole surface an even convexity, with 

 the exception of a narrow strip in the middle, which extends from beak to 

 base, and which is slightly depressed. This mesial depression is deepest in its 

 middle portion; it is only faintly marked upon the umbo, and it becomes 

 shallower but wider towards the base. The surface of both valves is orna- 

 mented by fine, thread-like radiating striae, which increase in number, partly 

 by bifurcation, but mostly by intercalation ; these radii are crossed by several 

 concentric lines of growth, which become more numerous towards basal mar- 

 gin. In regard to size, the specimen illustrated on plate 17, figures 30, 31 and 

 32, is of about the average size, though a few specimens have been found which 

 are considerably larger. 



Formation and Locality. Pound mostly in the rotten hornstone in upper strata of the Devonian 

 formation at the Falls of the Ohio. This species I name in honor of Prof. A. C. Goodwin, formerly of 

 Charlestown, Indians, an ardent collector. 



Orthis hybrida. SOWKBBY. 



Plate XXXII., figures 32 to 35. 



Orthis hybrida, Sowerby. Murch. Sil. Syst., p. 6301839. 

 Orthis hybrida, Hall. Geol. Kep. 4th dist., page 1071843. 

 Orthis hybrida, Hall. Pal. N. Y., Vol. III., p. 2531852. 

 Orthis hybrida, Hall, llth Rep. of Indiana, p. 2841881. 



Shell small, lenticular or depressed spheroidal, wider than long, valves nearly 



