Fic. 
PLATE XXXIV. 
SILURIAN SPECIES. 
1—1l2<a. Orthis flabellulum, Sow. 1. Perfect specimen. 2. Profile view of both 
13—22, 
29 
rustica, Sow. 
valves. 3. Ventral valve, with part of the internal 
cast seen. 4. Dorsal valve, showing the bifur- 
cation (and even trifurcation) of the ribs near the 
margin. 5. Dorsal valve. 6. Ventral valve, with ribs 
bifurcated. 7. Var. multifida, Salter. 8. Dorsal valve. 
9. Internal cast of dorsal valve. 10. Interior of the same 
valve. 11, 12. Internal casts of ventral valve. 12a. 
Interior of the ventral valve, enlarged, showing well the 
muscular and vascular impressions. All these specimens 
are from the Caradoc Sandstone of Boduan, Carnarvon- 
shire, and are drawn mostly from specimens in the 
Museum of the Geological Survey, and of which a few 
had also been previously figured by Salter in 2nd vol. of 
the ‘ Memoirs Geol. Survey.’ 12 a is froma fine internal 
cast in the Woodwardian Museum, Cambridge. 
12, 14, 15. Wenlock Limestone; Rushall Canal, near 
Walsall. 16. Interior of ventral; 17, of dorsal valve. 
Same locality. 18, 19. Var. rigida, Dav.  Benthall 
Edge. 20—22. Var. Walsalliensis, Dav. 20. From 
Rushall Canal. 21. From Buildwas, near Wenlock. 
22. Interior of dorsal valve. 22a. A portion of the 
shell, enlarged. 
