Pr.ATK XXXTX-Coiitlnaed. 



Gknus CYRTINA, Davioson. 



rage 43. 

 8«e Plates 25, 28. 

 Cyktina, sp. ? 

 Fi(f. 25. An enlarg«iueiit of the surface ; showing the bases of concentric rows of spinules. X 4. 

 Fig. 26. Caiilinal view of an internal cast of the pedicle- valve, bi-oken so as to show the convergent dental 

 plates uniting with the median septum, and the slight projection of the edge of the latter within 

 the spondyliuni thus formed. 

 Fig. 27. The same B))ccimen viewed from above j showing the length of the median septum. 

 Fig. 28. An enlargement of a portion of the interior of the pedicle-valve ; showing the convergence of the 

 dental plates, and the pi-ojection of the median sejitnm beyond their union. X 3. 

 Chert-beds of the Burlington limestone. Burlington, finoa. 



GENU8 SYRINGOTHYRIS, VVinchell. 



Pago 47. 

 See Plates 25, 26, 27. 



Sykingothyris Missouri, sp. iiov. 



Figs. 29-31. Three views of the typical sjiecimen ; showing its small size, elevated pedicle-valve, broadly 

 rounded cardinal margins, and coarse lateral plications. Internally this shell has the syringo- 

 thyi-oid tubiferous |)late, and the shell-substance is highly punctate. 

 Cboteau limestone. Pike county, Missouri. 



Genus CYRTIA, Dalman. 



Page 40. 



See Plates 21, 25, 26, 28. 



Cyrtia exporrecta, \Vtihlenl)eig, v:ii-. arrecta, Hall iiiul Whitfield. 



See Plate 28. 

 Fig. 32. View of the umbonal cavity of the conjoined valves ; showing the foramen, the strong dental 

 plates, and the articulating apparatus. X 2. 



Niagara group. Louisville, Kentucky. 



Cyrtia radians, sp. iiov. 



Pig. 33. Internal cast of a large specimen ; showing the general contour of the pedicle-valve, the impres- 

 sion of its dental plates and low median septum. 

 Niagara group. Milwaukee, WiscoTisin. 



Cyrtia simplex, Philliiw. 



Pigs. 34, 35. Cardinal and profile views of an entire in<lividual of average size ; showing the i-ecumbent 



cardinal area and the unplicatt'd surface. 

 Fig. 36. An enlargement of the surface of the same specimen ; showing the fine radial lines, which are 



interrupted concentrically and produced into shorf spinules. X 10. 

 Middle Devonian, Bredelar, Westphcdia. 



Cyrtia alta, Hall. 



See Plate 26. 

 Pig. 87. The cardinal area of the pedicle-valve j showing the vertical striation by the shell canals, and 



retaining the deltidial covering. 

 Fig. 38. Protile of a pe<licle-valve in its normal position ; showing the inclination of the cardinal area. In- 

 cipient plications are also seen al>out the anterior margins of the valve. 

 Chemung gi"onp. Meadville, Pennxylvania. 



Genus SPIRIFER, Sowerby. 



I'atre I. 



Spirifer acuminatus, Coiiiad. 

 Figs. 39, 40. Profile and cardinal views of a normal example ; showing the sharply elevated median fold and 

 the duplicate plications. 



Comiferous limestone. Sandusky, Ohio. 

 Pig. 41. Internal cast of a large pedicle-valve ; showing the size and composition of the muscular area. 



Hamilton shales. Haxtem New York. 

 Fig. 42. Internal cast of the central cardinal portion of the brachial valve ; showing the impi'CBsion of the 

 deejily striated cavity i-epresenting the cardinal process, the position of the cardinal area, 

 dental sockets and socket-walls. X 4. 



Comiferous limestone. Hanover, Indiana. 



