I—5. 
10. 
13—24, 
PLATE XXVIII. 
SILURIAN SPECIES. 
Orthis lunata, Sow. 1. Upper Ludlow; Wonder, Woolhope. 2. Internal and external casts. 
Upper Ludlow ; Whitecliffe, near Ludlow. 3. Internal cast of dorsal valve, 
enlarged. 3a. A gutta-percha impression, taken from the same cast, and 
enlarged. Upper Ludlow; Wonder, Woolhope. Coll. of Geol. Survey. 
4. Mould in gutta-percha, from an internal cast (4 @) of the ventral 
valve; both enlarged. Coll. of Geol. Surv. 5. Interior of ventral valve. 
Ludlow. 
redux, Barrande? Lower Silurian ; Budleigh Salterton, Devonshire. 6. Complete form, 
taken with gutta-percha from an external cast. 7. Internal casts. 8. Interior 
of ventral valve; 8a, of dorsal valve. 9. Internal cast of dorsal valve. 
These last three figures are enlarged. 
Girvaniensis, Dav. Caradoc ; Craig Head Quarry, Girvan, Ayrshire. 
elegantula, Dal. (O. canalis, M‘Coy). From moulds in gutta-percha, taken from internal 
casts. Kilbride, Cong. In the Collection of Sir R. Griffith, 
parva, Pander? According to M‘Coy. From Egool, Ballaghaderreen. Sir R. Griffith’s 
Collection. 
testudinaria, Dalman. 13. Caradoc; Grug, Llandeilo. 14—19. Different specimens figured 
by Mr. Salter in vols. ii and iii of the ‘Memoirs of the Geol. Survey,’ from the 
Caradoc of Cheney Longville; Cefn Rhyddan, &c. 20. Internal cast of 
ventral valve, enlarged. Caradoc; Narberth. 21. Interior of the same 
valve. Llandeilo Flags; Pantdwfn, Carmarthenshire. 2! a. Interior of 
dorsal valve, enlarged. 22. Internal cast of ventral valve, from Gorrans, 
Cornwall (Llandeilo Flags). 23, 24. After Mr. Salter’s figures. From 
Durness, Sutherlandshire ; in Llandeilo Flags. All these specimens are in 
the Museum of the Geological Survey. 
