46 BRITISH CARBONIFEROUS BRACHIOPODA. 



are evidently malformations, the beak being twisted more to the one than to the other 

 side, as well as otherwise misshaped. The regular convexity and smoothness of the 

 mesial fold and sinus distinguish the species under description from Sp. distans of 

 Sowerby, as will be shortly explained. 



Loc. This species occurs plentifully in various localities, such as in the lower Carbo- 

 niferous limestone of Castleton (Derbyshire), at Twiston (Lancashire), at Preston, Bolland, 

 Settle, near Bristol, &c. Mr. Kelly mentions the shell from Lisnapaste, Millecent, 

 Ballyduff, Malahide, Cork, &c, in Ireland. I have not yet seen any Scotch example. 

 In Belgium it is found at Tournay, and in other Continental localities. 



Spirifera distans, Sowerby. Plate VIII, figs. 1 — 17. 



Spirifer distans, J. de C. Sowerby. Tab. 494, fig. 3, May, 1825. 

 — — Phillips. Geol. Yorkshire, vol. ii, p. 217, 1836. 



Cyrtia distans, M'Coy. Synopsis of the Carb. Fossils of Ireland, p. 136, 1844. 



Spec. Char. Very variable in shape and proportions, more often imperfectly rhom- 

 boidal and transverse, with unequal convex valves. Hinge-line as long as the greatest 

 width of the shell. The dorsal valve is more or less convex, but not in general gibbous ; 

 semicircular, and somewhat indented in front. The lateral margins form a convex curve 

 to within a short distance of the cardinal angles, where they are often prolonged with acute 

 terminations. The fold is wide, and but little elevated, its upper surface being much 

 flattened, with a longitudinal sulcus extending along its middle, either quite to the front, 

 or soon becoming converted into a rounded central rib. The lateral portions of the shell, 

 on either side of the fold, are ornamented by from fourteen to fifteen small, single, or 

 bifurcated ribs. The ventral valve is much deeper than the opposite one ; the area is 

 triangular and variable in its proportions, as well as in its development ; it either presents 

 a large flat surface at right angles to the level of the dorsal valve, or is more or less 

 concave and elevated, showing or not a portion of the beak above and beyond its angular 

 termination. The fissure is narrow, and in great part covered by a convex pseudo- 

 deltidium. The sinus is of moderate depth, and, in general, exhibits along its centre a 

 well-defined rib, which is larger than those which ornament both slopes of the sinus and 

 lateral portions of the valve. In the interior of the ventral valve there exists two largely 

 developed, diverging, dental or rostral shelly plates, which extend from the beak along the 

 bottom of the shell to rather less than half its length. The dimensions are exceedingly 

 variable, on account of the great difference in depth of the ventral valve, as may be 

 perceived from the following measurements : 



Length 13, width 18^, depth 13 lines (Sowerby's type). 



„ 14, „ 21, „ 13 lines. 



„ 9, „ 22, ,, 14 lines. 



