
Gk 
Gk 
Gk 
Gk 
Gk 


LOWER BALA GROUP. 


Reference to McCoy's 
Synopsis : and Figures of Genera. 

Spirifera, p. 192. 
O. parva, p. 221. 


Names and References; Observations, &c. 
Numbers and Localities. 

Siphonotreta micula, McCoy (Davidson, Mon. 
Sil. Brach. pl. 8, figs. 2—6). A pretty small 
Brachiopod, covered with spines, and very 
nearly allied to the Discinw. Larger spe- 
cies, with thicker shells, occur in the Lower 
Bala rocks of Russia and Sweden. Also in 
the Upper Silurian of Britain. 
Orthis biforata, Schlotheim: a variety with fine 
ribs. This common species occurs over all 
the northern hemisphere. 
Orthis elegantula, var. parva, Pander. A va- 
riety only of the commonest of all British 
species of Orthis. It is comparatively rare 
in Lower Bala. 
{Orthis striatula, Emmons (Mem. Geol. Surv. 
Vol. 11. pl. 13, figs. 10—14) ]. 
Orthis calligramma, Dalm. (Mem. Geol. Surv. 
Vol. 1. pl. 22, fig. 1). This common shell 
ranges from Russia to Britain; and from 
the Arenig to the Wenlock rocks, 
Orthis turgida, McCoy. <A species with a 
remarkably tumid upper valve. 
Orthis confinis, Salter (Quart. Jour. Geol. Soe. 
v. t. 1, fig. 4, Davidson, 1. ¢. pl. 36, figs. 1—4). 
A large transverse species, with fine ribs. 
Is O. sagittifera the same species ? 
Strophomena, Rafinesque, Davidson, Salter. 
Differs from Orthis by having a widely 
expanded thin shell, and the cardinal pro- 
cess double. 
Strophomena concentrica, Portlock, Geol. Rep. 
p: 452. <A shell extremely common in the 
Caradoc or Middle Bala rocks. 
Strophomena, sp. (S. expansa, McCoy in part). 
A very flat species, with a much thinner 
shell than Sowerby’s Stroph. (Orthis) ex- 
pansa. The latter is a Middle Bala sp.— 
this is a common Lower Bala one. 


a. 102, Pen Cerrig, and 
Wellfield, near Builth, 
Radnorshire. 
a. 100, Tregib, Llandeilo. 
Rare in Lower Bala. 
Nant-yr-Arian, Llandeilo. 
Common in Lower Bala. 
Tan-y-graig, Builth (in vol- 
canic grit). a. 98, Cerrig 
Cregyn, Anglesea (quoted 
p. 215, as Upper Bala). 
Golden Grove, Llandeilo, 
in grit (also quoted as 
Upper Bala). Llandeilo. 
a. 99, Craig-y-beri, Llan- 
armon, N. Wales. a. 96, 
Bugon, Knockdollian, Ayr- 
shire. Llandeilo. 
Craig-y-beri, and Y Foel 
fawr, N. of Llanrhaidr, 
a. 105, Nant-yr-Arian, 
Llandeilo. 
