PLATE L. 



SILURIAN SPECIES. 



Fig. 

 1 — 14. Obolella sagittalis, Salter. Modifications in shape and stages of growth. 



Menevian rocks of St. David's, and Mawddach Water- 

 fall, Dolgelly. The smaller figures are of natural size. 

 1. Exterior, :2, 9, 11, 12, 14, interiors and internal 

 casts, of the ventral valve. 3 — 7. Ditto of the dorsal 

 valve. 



1-5 — 17. ;, ,, var. ^c///, Dav. Lower Tremadoc Slates ; Craig-y-dinas, 



North Wales. 15«, 16«, 17«. Enlarged. 



18 — 21. „ maculata, Hicks. Maenevian group, Porth-y-rhaw, St. David's, 



South Wales, and Gwynfynydd and Camlan, North 

 Wales. The smaller figures are of the natural size. 

 .23, 24. Obolus ? plumbeus, Salter, sp. 23. Interior; from the Lower Llandeilo of 



Shelve. 24. Exterior; from Wellfield, Builth. The 

 smaller figures are of the natural size. 



22. „ „ var. plicata, Hicks. Lower Arenig Rocks; Treman- 



here, St. David's. The smaller figure is of the natural 

 size. 



25. Kortuyina cingulata, Billings (named " Obolella ? Fhillijmi' at p. 62 and in 



pi. iv, figs. 17 — 19, of this Monograph). Malvern. 



26. Discina, sp. From the Graptolite Shale of Graple Linn, near Moffat, Scot- 



land. Dr. Nicholson's Collection. 



27. ,, ,, From the Bala Limestone of Keisley, Westmoreland. Prof. 



Harkness's Collection. The small figure is of natural 

 size. 

 2b. „ „ Upper Llandeilo beds of Gilwern, Llandrendod. Dr. C. Ricketts' 



Collection. 



