PLATE XCV 



PAGE 



Figs. 1-3. APARCHITES GORDON: Ulrich and Bassler n. sp 515 



1. Lateral view of left valve. X 20. 



2, 3. Longitudinal and vertical sections of same. X 20. 



Helderberg formation, Keyser member, Cumberland. 



Fig. 4. PRIMITIA POSTTURGIDA Ulrich and Bassler n. sp 515 



The unique right valve on which this species is founded, showing the 

 flattened anterior spine and the posterior marginal swelling. 

 X 20. Oriskany formation, 21st Bridge. 



Fig. 5, PRIMITIA ? CUMBERLANDICA Ulrich and Bassler n. sp 516 



A left valve showing the subcentral pit, strongly reticulated surface 

 and elevated rim. X 20. Helderberg formation, Keyser mem- 

 ber, Cumberland. 



Figs. 6-8. PRIMITIA ? CONCENTRICA Ulrich and Bassler n. sp 517 



Lateral, dorsal, and anterior views of a right valve. X 20. Oriskany 

 formation, 21st Bridge. 



Figs. 9, 10. PRIMITIELLA VARIOLATA Ulrich and Bassler n. sp 518 



Lateral and dorsal edge views of a right valve. X 20. Oriskany forma- 

 tion, 21st Bridge. 



Fig. 11. ULRICHIA A:QUALIS Ulrich and Bassler n. sp 518 



Right valve showing the usual form and obscure surface reticulation. 

 X 20. Oriskany formation, 21st Bridge. 



Figs. 12-15. STREPULA IRREGULARIS Jones and Holl 519 



12. An incomplete large left valve. X 20. 



13, 14. Two right valves of the average size showing differences in the 



surface ornament and outline. X 20. 

 15. Ventral edge view of original of fig. 13. X 20. 



Fig. 16. HALLIELLA ? SEMINULUM VAR. LONGA Ulrich and Bassler n. var. . . 520 

 A right valve slightly injured along the margin. X 20. Helderberg 

 formation, Keyser member, Cumberland. 



Figs. 17, 18. HALLIELLA ? TRIPLICATA Ulrich and Bassler n. sp 521 



17. Right valve. X 20. 



18. End view of same. X 20. 



Helderberg formation, Keyser member, Cumberland. 



Figs. 19-21. JECHMINA CUSPIDATA Jones and Holl 521 



19. Left valve showing the extraordinary development of the spine. 



X 20. 



20. 21. Lateral and anterior end views of a right valve. The variation 



shown in outline of body of valve is probably due to accident. 

 X 20. 

 Helderberg formation, New Scotland member, 21st Bridge. 



Figs. 22-24. MESOMPHALUS HARTLEYI Ulrich and Bassler n. gen. and sp. . . 523 



22. Lateral view of right valve showing the ventral swelling. X 20. 



23. An average right valve without the ventral pouch. X 20. 



24. Left valve of a rather small complete carapace. X 20. 



Helderberg formation, Keyser member, Cumberland. 



