266 BRITISH SILURIAN BRACHIOPODA. 



of the shell ; from fourteen to seventeen may be comited in two lines, at four lines from the 



beak " 



Length 9, width 11, depth 1^ lines. 



Obs. The internal details are so like those in 0. aiter?tafa that they need not be here 

 repeated. Prof. M'Coy attaches great importance to the backward curving of many of 

 the lateral striae to terminate on the hinge-line, and observes that something of the same 

 sort may be seen in a less degree in 0. sudquadrata, Hall. 



Position and Locality. This variety is said to occur in great profusion in the Caradoc 

 or Bala Flags of south end of Pen-y-Gaer, near Cerrig-y-Druidion ; and Prof. M'Coy 

 mentions it, also, as closely covering extensive surfaces of the beds on the Holyhead Road, 

 Denbighshire ; he quotes it also from Bala Flags at Hafod Evan, Penmachno, Caernar- 

 vonshire, also from the Bala Schists of Cefn-y-Coed, Llangedwyn, Montgomeryshire, and 

 from many other localities in the same county, and in Merionethshire, of which he 

 appends a list. 



Mr. Davies, of Oswestry, who has so attentively explored the rocks of North Wales, 

 informs me that the enumeration of localities in Sedgwick and M'Coy's ' Palaeozoic Rocks 

 and Fossils ' constitutes an admirable guide-book to the Silurian fossils of North Wales, 

 but that we must not forget that since 1834-38 the surface of the country in Wales has 

 undergone very great alterations ; for rocky escarpments covered with fossiliferous blocks 

 have been planted and enclosed, wide tracts of mountain- moorland have been made into 

 fields, the loose stones being buried or built into walls, and that quarries, once worked, as 

 in the neighbourhood of Bala, have been abandoned and covered with debris. 



Orthis confinis, Salter. PI. XXXVI, figs. 1 — 4. 



Orthis confinis, Salter. Quart. Journ. Geol. Soc, vol. v, p. 1.5, pi. i, fig. 4, 1848; 

 and vol. vii, pi. vii, fig. 5, 1851. 

 _ _ M'Coy. Brit. Pal. Foss., p. 215, 1852. 



— — Salter. Siluria, 4th ed., p. 526, 1867. 



Spec. Char. Subquadrate or transversely semicircular, depressed ; hinge-line slightly 

 less than the width of shell. Dorsal valve gently convex, and rather more so than in the 

 ventral one ; this last being slightly longitudinally keeled along the middle, while a 

 corresponding channel or depression in the dorsal one extends down the middle 

 line from the umbone to about half the length of the valve. Area in the ventral valve 

 narrow, vertical ; narrower in the dorsal valve ; fissure open ; beak scarcely projecting. 

 Both valves are closely covered with numerous radiating, thread-like striae, some being a 

 little stronger than others ; the riblets increase likewise in number by bifurcation and 

 interpolation, and often fasciculate in twos or threes. In the interior the muscular scars 

 are rather small. 



Length 10, width 13, depth 4 fines. 



