PLATE 18 



Figs. Heterorthina fairmountensis (Foerste) 

 1. — Ventral interior, showing widely divergent diductor 

 impressions and delicate pallial markings, x 2. Cf. 

 pi. 17, fig. 17. 

 2, 3. — Dorsal and ventral exteriors, x 1.5. 

 4. — Dorsal interior, to show cardinalia and musculature. 

 Notice lobed myophore and cleft shaft of cardinal 

 process, and simple divergent brachiophores. Cf. 

 fig. 7. x2. 

 Ordovician (Bellevue), Hamilton, Ohio. Cat. No. 

 S852. 



Heterorthina praeculta Bancroft 



5. — Ventral exterior, showing form of valve. 



Ordovician (Marshbrookian), Horderley District, E. 

 Shropshire, England. Cat. No. S 21 17. x 1.5. 

 6, 7. — Internal mold of dorsal valve and wax replica made 

 from it. Compare this replica with fig. 4; the 

 former shows the same cleft shaft and lobate myo- 

 phore, similar brachiophores, muscle impressions, and 

 pallial marks. 

 8. — Replica of a dorsal external mold. Dorsal valve flat 

 and shell multicosteUate. 

 Ordovician (Marshbrookian, Wattsella uiattsi zone), 

 Horderley District, E. Shropshire, England. Cat. 

 No. S2116. X 1.5. 



Cariniferella carinata (Hall) 

 9. — Ventral internal mold, showing muscle field and form 



of muscle impressions. 

 15. — Dorsal internal mold, showing impressions left by 



brachiophores and cardinal process. 

 16. — ^Wax impression taken from above. 



Devonian (Chemung), Bath, N. Y. Cat. No. 

 S1087. X 1.5. 

 10, 12. — Ventral and dorsal exteriors, showing prominent 

 dorsal sulcus and ventral fold. 

 Devonian (Chemung), Arkport, N. Y. Cat. No. 

 8 1088. X 1.5. 



Cariniferella dumonti (Verneuil) 



1 1 . — ^Ventral interior, showing musculature. 



Up. Devonian, ? Belgium. Mas. Comp. Zool., Har- 

 vard Coll. xl.5. 



Linoporella punctata (Verneuil) 

 13, 14, 18. — Ventral interiors, showing respective stages in 

 development of pseudospondylium. Fig. 1 8 shows 

 discrete dental plates with little or no adventitious 

 thickening on floor of delthyrial cavity. Fig. 14 

 shows an advanced stage in which the deposit is ele- 

 vated at the front and unites the dental plates, x 2. 

 Silurian (Gotlandian), Visby, Gotland, Sweden. 

 Riks. Pal. Zool. Avd., Stockholm. 



Figs. Linoporella punctata (Verneuil) — Cont. 

 24. — Reverse side of exterior in fig. 3 3, showing well inter- 

 area, teeth, dental plates, and median ridge, x 1.5. 

 33. — Exterior of a large ventral valve, showing characteris- 

 tic ornamentation, x 1.5. 

 Silurian (Gotlandian), Visby, Gotland, Sweden. 

 Riks. Pal. Zool. Avd., Stockholm. 

 17. — Posterior portion of large dorsal valve, showing car- 

 dinalia. Note extremely slender shaft of cardinal 

 process, with its thickened unlobed myophore. Brach- 

 iophore plates uniting below with median septum to 

 form a cruralium. 

 Silurian (Gotlandian), Foro, Lausa, Sweden, x 2. 



Levenea subcarinata (Hall) 



19,32. — Dorsal interiors, the former, x 1.5, showing ad- 

 ventitious growths on inside of brachiophores, and the 

 latter, x 2, showing well musculature and pallial marks. 

 31. — Ventral interior, showing characteristic musculature. 

 X 1.5. 

 Devonian (Birdsong), Birdsong Creek, west Ten- 

 nessee. Cat. No. S982. 

 20. — Enlargement of fig. 28, x 3. 



28. — Dorsal interior, turned slightly to the side, showing 

 unmodified brachiophores in the form of flat, ob- 

 liquely placed blades, x 1.5. 

 Devonian (Helderberg). Albany Co., N. Y. Cat. 

 No. S 986. 

 21. — Dorsal interior, showing greatly modified interior. 

 Shaft of cardinal process modified by a process grow- 

 ing forward from median lobe of myophore, brachio- 

 phores coated on inside by adventitious material which 

 cements them to the valve. Lateral pallial sinuses 

 given off between adductor impressions clearly visible. 

 Devonian (Birdsong), near Holladay, Tenn. Cat. 

 No. S 980. xl.5. 

 23. — Dorsal interior of young individual, showing brachio- 

 phores as simple, unmodified, oblique blades, x 1.5. 

 25, 29. — View, x 1.5, and its enlargement, x 3.5, to show 

 modified brachiophores, a line of demarcation be- 

 tween actual plates and adventitious substance being 

 clearly visible. 

 Devonian (Birdsong) Conrad Place, near Jeanette, 

 Tenn. Cat. No. S 988. 

 30. — Ventral internal mold, showing pentagonal form of 

 muscle field and pallial markings. 

 Devonian (Helderberg), near Clarksville, N. Y. 

 Cat. No. S 1014. X 1.5. 



Levenea cf. subcarinata (Hall) 



22, 26, 27. — Posterior, ventral, and dorsal exterior views. 

 Devonian (Birdsong), Benton Co., Tennessee. Cat. 

 No. 9719 Y. P. M. X 1.5. 



230 



