34 EXPLANATION OF THE PLATES. 
Lower Llandovery rocks at Haverfordwest ; Mandinam, in Caermarthen- 
shire ; Mathyrafal, in Montgomeryshire, &c. Mem. Geol. Surv., vol. iii., 
p. 339. Ireland; in limestone of Caradoc-Bala age, Chair of Kildare. 
Fic. 8.—a-d. ORTHIS FLABELLULUM, Sowerby. 
Silurian System, p. 639, pl. xix., fig. 8, pl. xxi., fig. 8. 
a. Original. Dorsal valve. 
b. Profile view; showing relative position of valves. 
e. Original. Internal cast of dorsal valve. 
d. Internal cast of ventral valve ; all from Boduan, Caernarvonshire ; in brown 
calcareous rock. Mus. G. S. I. 
Carapoc.—Sil., fourth edition, p. 526. ‘Common in Caradoc sandstone.” 
Ibid., p. 193. “North Wales and Shropshire, everywhere in Caradoc 
rocks,” M.G.S., vol. iii., p. 338. It occurs also abundantly in rocks of 
the same age in Ireland. 
Fic. 9.—a-f. ORTHIS CALLIGRAMMA, Dalman. 
lng Sil. Syst., p. 639. 0. calligramma, Sil., fourth edition, pl. v., 
gs. 7, 8, 9. 
a. Original. Impression of outer surface of ventral valve, from 9 0. 
b. Original. Interior of ventral valve. 
c. Original. Impression of exterior dorsal valve, from 9 d. 
d. Original. Interior of dorsal valve. 
e. Original. Enlarged portion of surface, showing proportion of ‘ rib” to 
intermediate strie, crossed by fine transverse lines ; all from Caradoc rocks, 
Grangegeeth, Co. Meath; in hard dark green grit. Mus. Geol. Surv. Irel. 
f. Original. Var. virgata. Internal casts and impressions of both valves, 
on a slab of coarse grey Caradoc grit, from Anglesea. Mus. G. S. I. 
LLANDEILO TO WENLocxk is recorded in Sil., fourth edition, p. 526, as the 
geological range of this frequently recurring species; it is stated to be one 
of the species of Orthis everywhere abundant in British Lower Silurian lo- 
calities, as well as in North Wales and Ireland, occurring, though rarely, in 
the Wenlock limestone of Britain. Jbid., p. 193. For special localities, 
see Memoirs Geol. Surv. and Brit. Sil. Brach., p. 245. 
