286 ' BRITISH SILURIAN BRACHIOPODA. 



the muscular impressions much wider. I find the peculiar hoof-like form and other 

 characters of this little shell (unlike L. deltoidea) to be extremely constant." 



Position and Locality. Strophoniena imgula appears limited to the Caradoc or 

 Bala Limestone. Prof. M'Coy states his shell to be gregarious, and to occur in 

 extraordinary abundance, completely filling some beds of the limestone at Llansaintfraid, 

 Glyn Ceiriog, south of Llangollen, Denbighshire ; and the limestone of Selottyn Road, 

 south of Llangollen. It has been found by Mr. Davies at Pontyglyn-Diffws-smiles, west 

 of Cor wen. 



Strophomena imbrex, Pander (sp.), var. semiglobosa, Bav. PI. XLI, figs. 1 — 6. 



§ 1. Typical or geniculated variety {not Intherto found in Great Britain). 



Plectambonitis triangularis, Pl. imbkex, Pl. inversa, Pander. Beit. Geogn. 



Russl.,p. 91,&c., pi. 19, 

 figs. 11, 12, 13, 1830. 

 Leptjena imbrex, De Verneuil. Geol. Russia, vol. ii, p. 33, pl. xv, figs. 3 a, h, 1845. 

 Orthis — Von Buck. Mem. Soc. Geol. France, vol. iv, p. 223, pl. xii, fig. 

 37, 1840. 



— — Quenstedt. Handb. Petref., p. 489, 1851. 



LeptvENa — D'Eichwald. Lethsea Eossica, per anc, vol. i, p. 866, 1859. 



• § 2. Var. semif/lobosa, Dav. 



LeptyENA imbrex, De Verneuil. Geol. Russia, vol. ii, p. 230, pl. xv. fig. 3 c, 1845. 



— — Bav. London Geol. Journ., vol. i, p. 55, pl. 12, figs. 25 — 28, 



1847 ; and Bull. Soc. Geol. France, 2nd ser., vol. v, p. 318, pl. 

 iii, fig. 8, 1848. 



— _ De Verneuil. Bull. Soc. Geol. Fr., ser. 2, vol. v. p. 347, 1848. 

 Strophomena — Schmidt. Sil. Form. Ehstl. &c., in Archiv Nat. Liv. &c., vol. 2, 



p. 215, 1858. 



— _ Salter. Siluria, 3rd ed., p. 251, figs. 6—7, 1859. 



— — Lindstrom. Gotlands Brach., p. 372, 1860. 



— — Billings. Geol. Surv. Canada, Pal. Foss., vol. i, p. 128, fig. 106, 1865. 



Spec. Char. Broadly semicircular, as wide as long, or a little broader than wide ; 

 hinge-line straight, not quite as wide as the shell ; sides and front rounded ; cardinal 

 extremities either rectangular or obtusely angular. Ventral valve very convex or gibbous, 

 sometimes slightly geniculated, flattened at and near the cardinal extremities ; area 

 triangular, narrow ; fissure arched over by a pseudodeltidiura. Dorsal valve concave. 



