BRACHIOPODS. 63 



Orthis swallowi HALL. 



Plate xxxviil, flg. 5. 

 Orthis swallowi Hall, 1858: Geology Iowa, vol. I, p. 597, pi. xii, figs. 



5a-b. 



Orthis clarkensis Swallow, 1863 : Trans. St. Louis Acad. Sci., vol. II, p. 

 81. 



Shell very large, wider than long ; hinge-line long, but 

 somewhat shorter than greatest width of the valves ; cardinal 

 extremities rounded. Dorsal valve quite convex, with occa- 

 sionally obscure traces of a mesial sinus. Surface marked by 

 numerous closely arranged radiating lines and concentric lines 

 of growth. 



Horizon and localities. Lower Carboniferous, Burling: 

 ton limestone : Hannibal. 



Orthis burlingtonensis HALL. 



Plate xxxviii, fig. 7. 



Orthis michelina, var. burlingtonensis Hall, 1858: Geology Iowa, vol. I, 



p. 596, pi. xil, figs. 4a-b. 



Orthis thiemei White, 1860: Jour. Boston Soc. Nat. Hist., vol. VII, p. 231. 

 Orthis missouriensis Swallow, 1863: Trans. St. Louis Acad. Sci., vol. I, 



p. 639. ( Not Shumard 1855. ) 

 Orthis thiemei White, 1883: U. S. Geol. andGeog. Sur. Terr., 12th Ann. 



Rep., p. 164, pi. xli, figs. 4a-d. 



Shell rather small, appressed, subcircular, hinge-line rather 

 short. Dorsal valve somewhat deeper than the ventral. Sur- 

 face of both valves marked by fine radiating costae. 



Horizon and localities. Lower Carboniferous, Kinder- 

 hook beds : Louisiana, Hannibal ; Burlington ( Iowa ) ; Burling- 

 ton limestone : Sedalia, Ash Grove ( Greene county ), Spring- 

 field, Hannibal, Louisiana, Ste. Genevieve. 



Orthis keokuk HALL. 

 Orthis keokuk Hall, 1858: Geology Iowa, vol. I, p. 640, pi. xix, figs. 5a-b. 



Very large, with small radiating costae. 



Horizon and localities. Lower Carboniferous, Keokuk 

 limestone : Wayland ( Clark county ). 



