CARBONIFEROUS LIMESTONE BRACHIOPODA. 255 



the hinge-line from the abrupt contraction of the ears, which 

 are separated by an abrupt curve from the steeply sloped 

 sides ; front margin slightly elevated into a broad wave ex- 

 tending its whole width, no mesial furrow; entering valve 

 almost as concave as the receiving one is convex; cardinal 

 area about ten times wider than high ; substance of the shell 

 thick ; external surface of both valves perfectly smooth, or 

 under a strong lens, with minute concentric striae of growth 

 near the margin ; internal cast of receiving valve marked with 

 very large quincuncially arranged punctures, usually about 

 twice their diameter apart ; rostral portion divided by a nar- 

 row slit left by the mesial septum, extending less than one 

 half the length of the shell. Width of large specimen 4^ lines, 

 proportional length of receiving valve -^j^q, depth /q^^. 



This species has much the form of Leptcena [Chonetes) volva 

 (M^Coy), but is not so wide and is more gibbous : it is the only 

 carboniferous species I know at this date that has a smooth 

 surface. The measurements given above are from a large Irish 

 specimen in the collection from the limestone of Mount Rath, 

 the English ones being only 2 lines wide. 



Rare in the dark carboniferous limestone of Lowick, North- 

 umberland. 



{CoL University of Cambridge.) 



Leptcena {Chonetes) suhminima (M'^Coy). 



Desc, Rotundato-quadrate, length three-fourths or four-fifths 

 the width ; receiving valve very gibbous in the middle, greatest 

 depth a little behind the middle ; hinge-line as long as the 

 shell is wide, forming flattened ears, slightly acute from the 

 sigmoid outline of the sides, having three or four moderately 

 long slender spines on each side of the beak, extending back- 

 ward as usual in the plane of the margins ; front margin 

 moderately convex ; surface uniformly covered with close ob- 

 tuse striae once or twice branched, but nearly uniform in size 

 on all parts of the shell, and so fine that twelve at the margin 

 only occupy half a line, when decorticated the impressed lines 

 between the striae of the surface very coarsely punctured, 

 and the beak slit by the deep impression of the mesial sep- 

 tum extending half the length of the shell; entering valve 

 nearly as concave as the receiving one is convex; surface 

 similar in both valves, the striae being crossed by fine close 

 lines of growth. Average width li line; the depth seems 

 about half the width. 



This little species is so extremely like the Silurian Leptmia 



