BRACHIOPODA. 185 



Foramen large, usually filled with the trifid cardinal process. Surface finely striated; 

 striae somewhat in fascicles, abruptly bending upwards towards the hinge line. Ventral 

 valve with a small vascular impression."— Hall, 1859. 



Rhipidometta ellsworthi n. sp. 

 Plate 45, figures 17-39, 



Orthis hybrida? Meek and Worthen, 1868, 111. Geol. Surv., vol. Ill, p. 371, pi. 7, figa. 



7a-d. 



Description — Shell subquadrangular to transversely suboval in outline, valves about 

 equally convex, anterior border uninterrupted to emarginate, anterior line of junction 

 of valves straight to sinuate. Dorsal valve marked, medially, from beak to front by a 

 distinct, rounded depression flanked on each side by a distinct, rounded ridge; beak 

 inconspicuous, incurved. Ventral valve most convex posterior to middle; either marked, 

 medially, from beak toward, or to, anterior margin by an indistinct, rounded ridge 

 bordered on each side by an indistinct, rounded depression — ridge corresponds in posi- 

 tion with depression in dorsal valve, and depressions correspond with ridges on dorsal 

 valve, or marked, medially, from anterior margin posteriorly by a shallow depression 

 whose width at anterior margin approximates distance between apices of ridges of dorsal 

 valve at anterior border; beak prominent, incurved. Length of cardinal area half to 

 less than half width of shell, delthyrium comparatively large. Surface ornamented by 

 radiating costae — 3 to 4 in 1 mm. at anterior border — that increase by bifurcation, 

 crossed by concentric growth lines. 



Remarks — -This species most closely resembles R. discus (Hall). 



Meek and Worthen's material was obtained from the Bailey limestone at Bailey's 

 Landing, Perry County, Missouri. 



Rhipidometta melvillei n. sp. 

 • Plate 46, figures 1-17 



Description — Shell subpentagonal in outline, valves about equally convex, anterior 

 line of junction of valves straight to sinuate. Ventral valve most convex posterior to 

 middle; convexity of valve uninterrupted, or valve flattened, or shaliowly depressed, 

 medially, from anterior margin posteriorly; beak prominent, incurved over that of dorsal 

 valve. Dorsal valve flattened, or shaliowly depressed, medially, from beak toward, or 

 to, anterior margin; beak inconspicuous, incurved. Cardinal area equal to or greater 

 than half width of shell, delthyrium relatively large. Surface marked by radiating 

 costae — 4" in 1 mm. at anterior margin — that increase by bifurcation, crossed by con- 

 centric lines of growth. 



Remarks — This species is quite distinct. 



Genus Bilobites Linn 



Bilobites varica (Conrad) 

 Plate 46, figures 18-25 



Delthyris bilobata Conrad (not Orthis bilobata Sowerby), 1838, 2nd Ann. Rept. N. Y. 



Geol. Surv., pp. 112, 118. 

 Delthyris varica Conrad, 1842, Jour. Acad. Nat. Sci., Philadelphia, vol. VIII, p. 262, 



pi., 14 fig. 20. 

 Orthis varica, Hall 1859, Pal. N. Y., vol. Ill, p. 179, pi. XXIV, figs, la-i, k, 1861. 

 Orthis (Dicoelosia) varica Hall, 1883, Rept. State Geol. N. Y. for 1882, pi. XXXV, 



figs. 38-40. 



