PLATE 16 



Figs. Mystrophora areola (Quenstedt) 



1, 5. — Dorsal and ventral exteriors of a large specimen. 



Compare the ornamentation and contour with those of 

 Skenidium, pi. 13. 



2, 3, 4. — Dorsal, lateral, and ventral views of a smaller 



specimen. 

 Devonian (Givetian, crinoid bed), Gerolstein, Ger- 

 many. Cat. No. S 2 1 1 0. x2.7. 



Orthorhynchula ottawaensis (Billings) 

 6. — ^Ventral interior of a silicified specimen, showing long 

 dental plates. 

 9, 13. — Crural bases with ends of crural processes, which 

 are extremely long when present. 



Certain rhynchonelliform shells from Kentucky have 

 been referred to this species, but they should be placed 

 with Camerella. The Ottawa forms (topotypes) have 

 commonly been referred to Camerella but belong with 

 Orthorhynchula. ^'■Camerella" fanderi from Paquette 

 Rapids, an associate of C. ottawaensis, is neither a 

 Camerella nor an Orthorhynchula, but allies itself 

 with the spire-bearing genera. 



Ordovician (Black River), Paquette Rapids, Ottawa, 



Canada. Cat. No. S 809. x 2.7. 



Orthorhynchula linnejri (James) 

 12. — Silicified specimen from which the ventral valve has 



been broken, revealing the crural bases. 

 28, 29. — Dorsal and lateral exteriors. 



Ordovician (Maysville), Frankfort, Ky. Cat. No. 

 7539 Y. P.M. x2. 

 1 7. — Ventral view of exterior. 



30.- — Ventral interior, showing teeth, interarea, and outline 

 of muscular field. 

 Ordovician (Maysville), Colby, Clarke Co., Ky. 

 Cat. Nos. S 795 and S 796 (fig. 30). x 2. 



Kayserella lepida (Schnur) 



7, 8, 10. — Posterior, lateral, and ventral views of exterior. 

 Posterior view shows deltidium indistinctly. 

 Devonian (Eifelian), Gerolstein, Germany. Cat. 

 No. S2111. x2. 



p,G3. Taffia planoconvexa Butts 



11. — Dorsal interior, showing orthoid character of cardi- 

 nal ia. 



Low. Ordovician (Odenville), E. of Odenville, 



Alabama. U. S. Nat. Mus. 



Pomatotrema grandaeva (Billings) 



1 4, 1 9. — Dorsal and ventral exteriors. 



16, 23, 26, 31. — Ventral interiors, showing deltidium, den- 

 tal plates, internal lateral ovarian ridges, and a ridge 

 developed from the adductor impression. 

 18, 21. — Dorsal interiors, showing lateral ridges and simple 

 cardinal process. The specimen in fig. 21 was 

 actually in conjunction with that in fig. 16. 



Pomatotrema shows many resemblances to the Cli- 



tambonacea and, together with the members of the 



Clitambonitida:, has been placed in that superfamily. 



Ordovician (Beekmantown), Newfoundland. Cat. 



Nos. S 81 (fig. 18) and S 82. x 2.7. 



Pomatotrema muralis Ulrich and Cooper, n. sp. 



15. — Ventral interior. 



20. — Dorsal internal mold. Compare these figures with 

 those of P. grandava. 

 Ordovician (upper Canadian), Ardmore quad., 

 Okla. Wax impressions of specimens in U. S. Nat. 

 Mus., Cat. Nos. S 77 (fig. 20) and S 79. x 2.7. 



Planidorsa crassicostella Schuchert and Cooper, n. sp. 

 22, 27. — Posterior and ventral views of the holotype, the 

 former showing chilidial plates. 

 Ordovician (Chazy), Speer's Ferry, Virginia. Cat. 

 No. S 763. Fig. 22x1.35. 



Planidorsa bella Schuchert and Cooper 



24. — Dorsal exterior, x 1.35. 



25. — Ventral internal mold, showing musculature, which is 

 essentially dinorthoid but with unusually large ad- 

 juster scars. X 2. 

 Ordovician (Chazy), Washburn, Tenn. Holotype. 

 Cat. No. S. 764. 



226 



