PLATE 12 



Pics. Schizophorella fallax (Salter) 



1 , 9. — Ventral interiors, the former an internal mold, x 2, 

 and the latter an impression taken from it, x 1.5. 

 Cat. No. B 52133, Brit. Mus. Nat. Hist. 

 2. — Dorsal exterior, x 1.5, the external mold correspond- 

 ing to fig. 4. Cat. No. B 52123, Brit. Mus. Nat. 

 Hist. 

 3. —Ventral exterior, x 1.5. Cat. No. B 52121, Brit. 



Mus. Nat. Hist. 

 4. — Dorsal internal mold, x 2. Cat. No. B 44610, Brit. 



Mus. Nat. Hist. 

 7. — Impression from the above, x 1.5, showing support- 

 ing plates of brachiophores. 

 Ordovician (upper Bala, Drummock group. Starfish 

 bed), Thraive Glen, Girvan, Ayrshire, Scotland. 

 Cat. Nos. S 486 and S 487. Impressions of British 

 specimens. 



Mimella globosa (Willard) 

 5, 10, 14, 15. — Posterior, dorsal, lateral, and ventral views 

 of exterior. This species was previously referred to 

 Pionodema, with which it forms a heterochronous 

 homoeomorph. 

 Ordovician (Chazy), Luttrell, Tenn. Cat. No. 

 S483. X 1.5. 

 6. — ^Dorsal interior, showing septum, cardinal process, and 



sessile cruralium. 

 8. — Ventral interior, showing trilobed muscle area. 



Ordovician (Chazy), Washburn, Tenn. Cat. No. 

 S482. xl.5. 



Mimella melonica (Willard) 

 20. — Ventral interior, showing trilobed muscle field and 

 pallial markings. 

 Ordovician (Chazy), Luttrell, Tenn. Cat. No. 

 S474. xl.5. 



Mcewanella lineolata (Savage) 

 11, 12. — Ventral valve, the latter showing the interarea. 

 1 8, 22. — Dorsal exterior and interior. Brachiophores of 

 dorsal interior like those of Platystrofhia, and the 

 plates supporting them unite beneath the cardinal 

 process. 

 2 1 . — Ventral interior. Muscle-scars not defined and mus- 

 cle field with thickened peripheral rim. 

 Ordovician (Fernvale), old quarry S. of Regen- 

 hardt's quarry, N. W. edge of Cape Girardeau, 

 Missouri. Cat. No. 65872, U. S. Nat. Mus. x 1. 



Figs. Mcewanella raymondi Foerste 



17. — Ventral exterior, to show characteristic ornamentation. 



Ordovician (top of Kimmswick), Cape Girardeau, 



Missouri. U. S. Nat. Mus. x 1.5. 



Platystrophia crassa (James) 



13. — Dorsal interior, showing gerontic condition of car- 

 dinalia. 

 Ordovician (Maysville), Spring Valley, Minn. Cat. 

 No. S583. x 1.5. 



Platystrophia laticosta (Meek) 

 1 6. — Dorsal interior, showing incurving brachiophore plates 

 which are clearly visible only in young Platystrofhia. 

 Cf. Plectorthis, pi. 11, fig. 4. 

 23. — Ventral interior of young shell, showing dental plates 

 and muscle area. Dental plates not visible in gerontic 

 shells, see fig. 26. 

 27. — Dorsal interior, showing muscle impressions and car- 

 dinalia. The cardinal process of Platystrofhia is 

 usually much aborted. This figure shows the brachio- 

 phores and their supporting plates much thickened by 

 callus deposit. 

 Ordovician (Maysville), Cincinnati, Ohio. Cat. 

 No. S 575. xl.5. 



Platystrophia cf. laticosta (Meek) 



19. — Very young dorsal valve, showing strongly incurving 

 brachiophore plates and fulcral plates. Cf. similar 

 views of Plectorthis and Hebertella. 



Ordovician (Maysville), Roh's Hill, Cincinnati, 



Ohio. Cat. No. S 566. x 3. 



Platystrophia acutilirata (Conrad) 

 24. — Ventral interior of gerontic individual. Dental plates 

 obsolete and interior pitted by ovarian? impressions. 

 Ordovician (Whitewater), Oxford, Ohio. Cat. No. 

 S545. xl.5. 



Platystrophia ponderosa Foerste 



25. — Dorsal interior, showing a gerontic individual. Car- 

 dinalia so thickened as to obliterate fulcral plates and 

 exaggerate brachiophore supports, x 1.5. 

 26. — Gerontic ventral valve. Dental plates obsolete, owing 

 to filling in of umbonal cavities, x 1. 

 Ordovician (Maysville), Cincinnati, Ohio. Cat. 

 No. S5 56. 



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