PLATE 23 



Figs. Pionodema subsequata (Conrad) 



1, 5. — Ventral and dorsal views of the holotype. 



Ordovician (Black River), Mineral Point, Wis. 

 Cat. No. 694/3 Amer. Mus. Nat. Hist, x 2. 

 3. — Posterior view of exterior, x 1.5. 

 7. — Dorsal interior, showing flaring brachiophore plates 

 and thickenings extending forward from them. Cf. 

 figs. 2, 4. X 3. 

 Ordovician (Black River), near Lanesboro, Minn. 

 Cat. No. S 1 364. 



Pionodema redux (Barrande) 



2, 4. — Dorsal internal mold (fig. 4) and wax impression of 



it. Cf. fig. 7. Brachiophore plates separate, but low 

 ridges extend from them and converge toward the 

 median ridge. 



Ordovician (Dd), Mt. Drabow, Bohemia. Mus. 



Comp. Zool., Harvard Coll. x 1.5. 



Pionodema minnesotensis Cooper 



6, 10, 14. — Dorsal, ventral, and posterior views of the 

 holotype. Notice swollen ribs. 

 Ordovician (Black River), Minneapolis, Minn. 

 Cat. No. S 1356. x 1.5. 



Pionodema cf. circularis (Winchell) 

 8. — Dorsal interior, showing well the flaring brachiophore 

 plates. Cf. fig. 21. 

 Ordovician (Glade Is. of Safford (?))> Lebanon, 

 Tenn. Cat. No. S 1360. x 2. 



Pionodema cf. conradi (Winchell) 



9. — Ventral interior, showing musculature and apical plate. 

 Ordovician (Black River), St. Paul, Minn. Cat. 

 No. 1359 S. X 1.5. 



Pionodema uniplicata Cooper 



12. — External view of ventral exterior, showing deep 

 sulcus. 

 Ordovician (Black River), Minneapolis, Minn. 

 Cat. No. S 1361. x 1.5. 



Figs. Pionodema circularis (Winchell) 



13. — Incomplete dorsal valve turned to the side in order 

 to show the fulcral plate which defined the socket. 

 Cf. fig. 18. 

 Ordovician (Black River), 2.5 miles S. of High 

 Bridge, Ky. Cat. No. S 1348. x 3. 



Isorthis ? tuUiensis (Vanuxem) 



15, 19. — Ventral internal mold, and reverse side showing 

 dorsal interior. Pallial marks distinctly spread apart, 

 showing pattern clearly. 

 Devonian (Tully), Skaneateles, N. Y. Cat. No. 

 S1412. X 1.5. 



Schizophoria provulvaria Maurer 



1 1. — Dorsal internal mold, showing pallial trunks. 



Devonian, Seifen, Germany. Cat. No. S 1401. 



X 1. 



Schizophoria vulvaria (Schlotheim) 



16.— Ventral internal mold, showing exceedingly long di- 



ductor impressions separated by a long septum. 

 1 7. — Dorsal interior, showing pallial markings. 



Low. Devonian (Cobienzian), Laubach, Germany. 



Mus. Comp. Zool., Harvard Coll. x 1. 



Schizophoria iowensis (Hall) 



18. — Same specimen as in fig. 21, turned to side to show 



brachiophore supports and fulcral plates. 

 20. — Ventral interior, showing musculature and median 



fold which carries adductor impressions. 

 21. — Dorsal interior, showing flaring brachiophore plates, 

 fulcral plates, and musculature. 

 Up. Devonian, Rockford, Iowa. Cat. No. S 1441. 

 x2. 



Schizophoria aff. striatula (Schlotheim) 

 22-25. — Posterior, dorsal, lateral, and ventral views of ex- 

 terior. Compare fig. 24 with fig. 19 of pi. 11. 

 Devonian (Craghead Creek), E. of Toledo, Calla- 

 way Co., Missouri. Cat. No. S 1447. x 1. 



240 



