172 BRITISH SILURIAN BRACHIOPODA. 
Abberley, Leintwardine ; Dowlas, near Usk; Cwm-Craig-ddu and Erw Gilfach, Builth 
district. 
In the Wenlock Limestone and Shale, west of Rock Farm, May Hill, Dudley; near 
Walsall; east of Ledbury; Eastnor Gravel Pit; Witfield, Tortworth ; Comb Hill, Malvern; 
Clincher’s Mill; Scar Lime-works, Onibury. Bryn-Mawr; Mynydd-Tryfan ; and Capel-y- 
rhiw, North Wales (in beds above the Denbighshire Grit). 
In the Weoolhope Limestone at Little Hope Woolhope, Bogmine Shelve, and in the 
Llandovery at Tynewydd, Llandovery. 
In Scotland it occurs in the Wenlock Shale of the Pentland Hills, and in the same 
formation at Clogher Head, Kerry. 
Abroad it is abundant in the Island of Gothland; at Moustel-Pank, and at St, 
Johannis in the Island of Oesel, and in Russia; in the neighbourhood of Christiania, 
Norway. In America it is stated by M. de Verneuil to occur in the States of 
Tennessee and of the Ohio, where it is completely identical with the European 
specimens. 
RuyNncHoneLLa Wixsoni, var. Davipsoni, A/‘Coy. Pl. XXIII, figs. 11—14. 
TEREBRATULA SPHM@RICA, Dav. Bull. Soc. Géol. de France, 2nd ser., vol. v, 
p. 328, pl. iii, fig. 36, 1848 (of Géol. Trans., not of 
Sil. Syst.) 
Hemituyris Davipsoni, A‘Coy. Annals and Mag. of Nat. Hist., vol. vili, 2nd ser., 
p- 592, 1851; and British Paleozoic Fossils, p. 200, 1852. 
This variety differs from the typical forms of 2A. Wilsonc in having fewer and stronger 
ribs ; in other respects the general form is about the same, being subcuboidal, and usually 
slightly longer than wide, some examples having attained 13 lines in length, 12 in width, 
and 10 indepth; and of these a fine series, belonging to Mr. Fletcher’s collection, may be 
seen in the Woodwardian Museum, Cambridge. Prof. M‘Coy is, however, mistaken 
when he asserts that the ribs are not divided by a median sulcus, as in RA. Wilsoni ; for 
I have now before me several specimens in which the ribs are, in the proximity of the 
margin, divided by a median groove (see Pl. XXIII, figs. 12a and 12c.) It is true that 
in some examples (as is the case with typical RA. Vilsonz), the longitudinal grooves are not 
clearly observable, and may be entirely absent. The number of ribs varies also in 
different individuals, so that from three to six ribs may be counted on the slightly raised 
mesial fold, as well as on the shallow sinus; when the ribs are more numerous the form 
gradually merges into true RA. Wilsont. In 1848 I had referrred this form to the 
Terebratula spherica, Sow., so named by that author in Murchison’s and Sedgwick’s 
memoir “On the Physical Structure and Old Stratified Deposits of Devonshire” (‘Trans. 
Geol. Society,’ vol. v, pl. lvii, fig. 3, 1840), but I had overlooked the fact that the same 
