PLATE XX. 



ORTIIIS, Dalman. 



IPage 217. 



Orthis flabellites, Hall. 



(See Plate V. figs. 37-41.) 



Fig. 1. An interual cast of the jiedicle-valve ; showing- very distinctly the rhai-arter of the musi-ulai- scar, 

 and the simple plication of the surface. 



Niagara group. Hamiltmi, OntarioA 



Ortmis punctostriata, H;i1!. 



Page 217. 

 Figs. 2, 3. Two views of a slightly distorted indiviilual, retaining both valves. 



Fig. 4. An enlargement of the surface j showing the rows of superficial punctje between the strise. 

 Niagara group. Lochport, N. T. 



Orthis (Rhipidomella) Burlingtonensis, Hall. 



(See Plate VIa, fig. 13.) 

 Fig. 5. An exfoliated pedicle-valve ; showing very distinct impressions of the adductor and didnctor scar. 

 Fig. 6. Posterior view of the cardinal process and crural plates of the brachial valve. X 4. 

 Chert of the Bui-lington limestone. Pike county, Missouri. 



Orthis (Rhipidomella) Michelini, Leveill6. 



Fig. 7. The interior of the pedicle-valve ; after Davidson. (Bi-itish Carboniferous Brachiopoda, pi. xxx, 

 fig. 11.) 



Carboniferous limestone. Ayrshire. 



ORTHOTHETES, Fischer de Waldheim. 



Page 253. 



Orthothetes deformis, Hall, var. sinuata, var. iiov. 

 (See Plate IX, fig. 32.) 



Figs. 8, 9. Two views of a specimen ; showing the distortion of the beak and the median sinus on the bra- 

 valve, which is a characteristic featui-e of some species of Derbva. Further examination will 

 probably prove this form to be a distinct species. 



Lower Helderberg group. Cumberland, Md. 



DERBYA. VV^aagen. 



Page 261. 



Derbya Correana, Derby. 



(See Plate XI. figs. 18-22.) 



Figs. 10, 11. Two views of the umbonal portion of an internal cast of a pedicle-valve, broken to show the filling 

 of the umbonal cavity between the united dental plates. Fig. 10 also shows the impression of 

 the median septum supporting these plates. X 2. 

 Carboniferous limestone. Itaituha. Brazil. 



Derbya crassa, Meek and Haydeii. 



(See Plates X, XIb, XIc.) 



Figs. 12, 13. The interior of both valves of the same specimen ; showing the muscular scars, median septum 

 and cardinal process. 



Upper Coal Measures. Near Kansas City, Missouri. 



