PLATE 19 



Figs. Thiemella villenovia Williams 



1, 5. — Dorsal and ventral exterior views, showing well the 



reversion of fold and sulcus which is one of the 

 generic characters. The specimens figured are 

 squeezes of external molds in the U. S. Nat. Mus. 

 X 1.5. 



2, 6. — Ventral internal molds, showing musculature and 



long septum dividing anterior ends of diductor scars 

 and extending some distance in front of them. Fig. 

 2 X 1.5, fig. 6 X 2. 

 4. — Replica of dorsal internal mold, showing cardinalia. 

 X 1.5. Note delicacy of structures and compare with 

 the rather ponderous cardinalia of Aulacella, fig. 13. 

 9. — Dorsal internal mold, the reverse side of that in fig. 

 4. xl.5. 

 Devonian (Chemung), Dyes quarry, Villenova, 

 Chautauqua Co., N. Y. Originals in U. S. Nat. 

 Mus. 



Rhipidomella vanuxemi (Hall) 

 3. — ^External view of ventral valve, showing swollen 

 costellje. 

 Devonian (Hamilton), Canandaigua Lake, N. Y. 

 Cat. No. S 1286. X 1. 



Aulacella eifelensis (Verneuil) 

 7, 8. — Dorsal and ventral views of exterior, showing fold 



and sulcus, which are not reversible, x 1.5. 

 11. — Ventral internal mold, showing musculature. Ad jus- 

 tor impressions clearer in this specimen than usual. 

 Cf. the same view of Thiemella, fig. 6, and note that 

 whereas in Aulacella the septum forks at the ends of 

 the diductor scars, in Thiemella there is no forking 

 and the septum extends a considerable distance in 

 front of the muscle field, x 2. 

 Mid. Devonian, Eifel, Germany. Cat. No. S 1096. 



10. — Ventral interior, showing elongate muscle field with 

 diductor impressions separated by a low ridge which 

 forks in front, x 2. 

 13. — Dorsal interior, showing ponderous cardinalia which 

 have a strong resemblance to those of Rhifidomella. 

 Cf. fig. 4. xl.5. 

 Mid. Devonian, Eifel, Germany. Schultze Colls., 

 Mus. Comp. Zool., Harvard CoU. 



Perditocardinia dubia (Hall) 



12,20,22. — Lateral, dorsal, and ventral views of a large 



specimen, showing terebratuloid form of valves. 

 21. — Ventral interior, showing musculature. 



Mississippian (St. Louis), Spergen Hill, Ind. Cat. 



No. S 1300. x2. 

 16, 17. — Ventral and posterior views of exterior. 



Mississippian (Carthage), Webb City, Jasper Co., 



Missouri. Cat. No. S 1293. x 2. 



Figs. Perditocardinia aflf. P. dubia (Hall) 



14,15. — Ventral and dorsal interiors. Ventral interior 

 shows clearly the lack of an interarea and consequently 

 of a hinge-line. Dorsal interior shows ponderous 

 cardinalia similar to those of Rhifidomella but with 

 modifications induced by the compression of the inter- 

 area to disappearance. 

 Mississippian (Salem), near Valley Park, St. Louis 

 Co., Missouri. Cat. No. S 1297. x 2. 



Platyorthis planoconvexa (Hall) 

 18,19,29. — Dorsal, ventral, and lateral exterior views. 



Notice particularly planoconvex profile, x 1. 

 23. — Ventral interior, showing flaring dental plates con- 

 tinued as ridges along margins of muscle field, x 1.5. 

 24. — Dorsal interior of silicified specimen, showing pon- 

 derous cardinal process and oblique, bladelike brach- 

 iophores. xl.5. 

 Devonian (Oriskany), Cumberland, Md. Cat. No. 

 S114S. 



Platyorthis circularis (Sowerby) 

 27. — Dorsal internal mold. The pit marking the cardinal 

 process is short, showing a short cardinal process but 

 elevated a considerable distance in a ventral direction. 

 28. — Ventral internal mold, showing elongate flabellate ad- 

 justor-diductor fields separated by a median ridge 

 which carried the adductor muscles. 

 Devonian (Coblenzian), Siegen, Germany. Cat. 

 No. SI 139. xl.5. 



Platyorthis opercularis (Verneuil) 

 31. — Dorsal view of exterior, showing flatness of dorsal 

 valve. 

 Devonian (Eifelian), Gerolstein, Germany. Cat. 

 No. S 1141. xl.5. 



Proschizophoria personata (Zeiler) (emend. Kayser) 



25. — Dorsal internal mold. Cardinal process and brachio- 

 phore plates ponderous. Anterior adductor impres- 

 sions separated from posterior impressions by hori- 

 zontal ridges (in the mold, depressions). 

 30. — Ventral internal mold, showing subtriangular muscle 

 field. Diductor impressions long and adductor im- 

 pressions imprisoned within them. 

 Up. Devonian, Unkel, Germany. Schultze Colls., 

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



26, 32. — Ventral and dorsal internal molds. 



Low. Devonian (Siegenerschichten), Seifen, Ger- 

 many. Cat. Nos. S 1090 and S 1089. xl.5. 



232 



