ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 979 



Fig. 36a. Ditto. Outline side-view of same shell. x 2. 



Fig. 37. Ditto, var. Impression of exterior of brachial valve. x 2|. Balclatchie Group, Ardmillan. G. 



Fig. 38. Ditto, ditto, x 2. Same horizon and locality. G. 



Fig. 39. Ditto. Internal cast of same shell. x 2. 



Fig. 40. Orthis (P/ectort/iis) duftonensis, Reed, var. Impression of exterior of brachial valve. x 2. 



Balclatchie Group, Ardmillan. G. 



Fie. 41. Ditto. Internal cast of same shell, x 2. G. 

 6. J^tV- 



Plate VI. 



Fig. 1. Orthis (Plectorthis) duftonensis, Reed, var. Internal cast of brachial valve, x 2. Balclatchie 

 Group, Ardmillan. (Figured, Davidson, Suppl., pi. xiii, fig. 26.) G. 



Fig. 2. Ditto. Internal cast of pedicle-valve. x 2. Same horizon and locality. G. 



Fig. 3. Orthis (Plectorthis) rustica, Sow. Interior of pedicle-valve, x \\, Saugh Hill Group, Woodland 

 Point. G. 



Fig. 4. Ditto. Interior of brachial valve. x \\. Same horizon and locality. G. 



Fig. 5. Ditto. Interior of pedicle-valve, x 1|. Same horizon and locality. G. 



Fig. 6. Ditto. Internal cast of pedicle-valve. x 1£. Same horizon and locality. G. 



Fig. 7. Ditto. Internal cast of brachial valve. xl|. Same horizon and locality. G. 



Fig. 8. Ditto. Internal cast of pedicle-valve. x 1^. Same horizon and locality. G. 



Fig. 9. Orthis {Plectorthis) rustica, var. nov. paucicostata. Interior of brachial valve. x 1J. Saugh 

 Hill Group, Woodland Point. G. 



Fig. 10. Ditto, ditto. x lj. Same horizon and locality. G. 



Fig. 11. Ditto. Pedicle-valve. xl|. Same horizon and locality. G. 



Fig. 12. Ditto, ditto. x 1J. Same horizon and locality. G. 



Fig. 13. Orthis (Plectorthis) rustica, var. rigidu, Dav. Internal cast of pedicle-valve, x 2. Saugh Hill 

 Group, Woodland Point. G. 



Fig. 14. Ditto, ditto. x 2. Same horizon and locality. G. 



Fig. 15. Ditto. Interior of brachial valve. x 2. Same horizon and locality. G. 



Fig. 16. Ditto, ditto, x 2. Same horizon and locality. G. 



Fig. 17. Ditto. Exterior of brachial valve. x 2. Same horizon and locality. G. 



Fig. 18. Ditto, ditto. x 2. Same horizon and locality. G. 



Fig. 19. Ditto. Pedicle-valve. x 1|. Same horizon and locality. G. 



Fig. 20. Orthis (Plectorthis) rustica, var. walsalliensis, Dav. x 1£. Penkill Group, Penwhapple 

 Glen. G. 



Fig. 21. Orthis (Plectorthis) subfissicosta, sp. nov. Pedicle-valve. x 2. Stinchar Limestone Group, 

 Craighead. G. 



Fig. 22. Orthis (Plectorthis) subplicatella, sp. nov. Internal cast of pedicle-valve, x 2. Balclatchie 

 Group, Balclatchie. G. 



Fig. 23. Ditto. Portion of surface of shell (from squeeze), x 5. Same horizon and locality. G. 



Fig. 24. Ditto. Internal cast of brachial valve. x 1\. Same horizon, Ardmillan. G. 



Fig. 25. Ditto. Same shell (from squeeze of impression), x 2|. G. 



Fig. 26. Ditto. Internal cast of pedicle-valve, x 2. Same horizon, Balclatchie. G. 



Fig. 27. Orthis (Plectorthis) thraivensis, sp. nov. Pedicle-valve (from squeeze). xl|. Starfish Bed, 

 Drumrauck Group, Thraive Glen. G. 



Fig. 28. Ditto. Internal cast of pedicle- valve. x \\. Same horizon and locality. G. 



Fig. 29. Ditto. Internal cast of brachial valve. x 1J. Same horizon and locality. G. 



Fig. 30. Ditto, ditto. x \\. Same horizon and locality. G. 



Fig. 31. Ditto. Posterior view of internal cast of complete shell, x 2. Same horizon and locality. G. 



Fig. 32. Ditto. Portion of surface of shell (from squeeze). x 4. Same horizon and locality. G. 



TRANS. ROY SOC. ED1N., VOL. LI, PART IV (NO. 26). 139 



