PLATE XXXI. 
SILURIAN SPECIES. 
Fic. 
3s: Orthis alternata, Sow. 1, 2, 3. Caradoc; Pentre, Llymru, Llanfyllin. Mus. 
Geol. Survey. 4. Caradoc; Eglways Anne, north of Bala. 
Same Museum. 5. Internal cast of dorsal valve. 5a. In- 
terior of dorsal valve; from a gutta-percha mould taken 
from the cast and enlarged. 6. Internal cast of ventral 
valve. Caradoc; Ketch, Llanfyllin. 6 a. Interior of valve, 
taken in gutta-percha from internal cast and enlarged. 
7. Internal cast of dorsal valve, enlarged. From Cheney 
Longville. Mus. Geol. Survey. 8. Figure taken from an 
unpublished plate prepared by the Geol. Survey. The figure 
is enlarged, and shows the internal cast of both valves. 
9—1]1. , fallax, Salter. 9. After the origimal figure in the ‘Synopsis Sil. Foss. of 
Ireland.’ Caradoc; Desertcreat, Tyrone. Coll. of Sir R. 
Griffith. 11. From Killey, Pomeroy. Same Collection. 
10. Internal cast of ventral valve. Desertcreat. Mus. 
Geol. Survey. 
12—20. »  porcata, M‘Coy. 12. Coniston Limestone ; Coniston. Mus. Geol. Soc. 
13. Portrame, County Dublin. Mus. Geol. Survey of 
Ireland. 14. Moelydd, near Bala. 15. Internal cast of 
dorsal valve, after a figure by M‘Coy, in ‘ Brit. -Pal. Foss.’ 
Coniston. 16. Another figure, from the same work and the 
same locality. 17. Var. grandis, Portlock. Internal cast of 
ventral valve. 18. Var. cnflata, Salter. Coniston Lime- 
stone; Westmoreland. 19. Internal cast of dorsal valve. 
= 0. grandis, Pollock (not Sow.). Desertcreat, Tyrone. 
19 a. Interior of the same valve, from a gutta-percha im- 
pression taken from the cast. 20. Internal cast of ventral 
valve. Same locality. 20a. Interior, taken from the cast. 
Portlock’s original specimens in the Museum of the Geol. ° 
Survey. 
