178 BRITISH SILURIAN BRACHIOPODA. 
convex or gibbous. Ventral valve rather deeper than the dorsal one; beak small, 
incurved ; sinus wide, deep, with a small median rib; ribs on each of the lateral portions 
of the valve varying in number from five to seven. Dorsal valve divided by a wide, 
moderately elevated, biplicated fold, while from five to seven ribs ornament each of the 
lateral portions of the valve. Surface of both valves crossed by concentric lines of growth. 
Two specimens measured— 
Length 7, width 7, depth 6 lines. 
SVMEONOR,. b4 6.0 WB 
Obs. This species is easily recognisable on account of its wide biplicated fold and 
sinus, and small simple lateral ribs ; but it is a mistake to suppose that, as its name would 
imply, not more than ten ribs ornament the surface of each valve, for I have counted 
from ten to fifteen in different examples. It varies also much in size, but rarely exceeds 
the dimensions above given, and is often smaller. ‘The form to which it most approaches 
is Rhynchonella borealis, var. diodonta, but it is distinguished by its more numerous and 
smaller lateral ribs. 
Position and Locality. Although mentioned in ‘ Siluria’ as having been found in the 
Wenlock, I have not seen specimens derived from that formation. It is peculiar, as far 
as I know, to the Upper Llandovery (May Hill group of Sedgwick). One example, how- 
ever, which I cannot distinguish from the species under description, was sent to me by 
Mr. Davies from the Bala Limestone of Allt-y-gader, Llanfyllin, in North Wales 
(fig. 24). 
The following localities have been quoted, all in Upper Llandovery :—Mwdwl, 
Hithin, Plas Madoc, North Wales ; also Presteign, Malverns; Minton, Chirbury, Norbury. 
In Wales and Shropshire fine examples occur at the Obelisk, Eastnor Park. Phillips and 
Salter mention also, besides the above-named localities, under Worcester Beacon ; Wych ; 
Cowley Park, Malvern; Ankerdine Hill, Abberley district ; Lampeter Hill, Haverfordwest 
district, and Marloes Bay in the Marloes district, &c. 
I am not acquainted with the shell from either Scotland or Ireland, and have not seen 
any foreign specimen. 
RHYNCHONELLA DEFLEXA, Sow. PI. XXII, figs. 24—27. 
TEREBRATULA DEFLEXA, J. de C. Sow. Sil. Syst., pl, xii, fig. 14, 1839. 
— BREVIROsSTRIS, Id. Ibe, pl. xin, fig, 15. 
—- SPHHRICA, Id. ib. pleodi, Ae. l7- 
— INTERPLICATA, Id. Ib., pl. xii, fig. 23. 
— DEFLEXA, Barrande. Brachiopoda of Bohemia, Naturwissens. Abhandl., 
pl. xx, fig. 15, 1847. 
— DEFLEXA et SPH#RICA, Dav. Bull. Soc. Géol. France, 2nd ser., vol. v, 
p. 328, 1848. 
— — De Verneuil. Ib., p. 346, 1848. 
