236 CAMBRO-SILURIAN fOSSILS. 



deflection or arching of the valves, also separate it from the 

 S. grandis. 



The specimens from Blain y cwm and Golden Grove are netted 

 by a beautiful little species of Vioa branching frequently, nearly 

 at right angles, forming straight, forking or angularly bending 

 channels, one-fourth of a millimetre in diameter, the branches 

 being at a little more or less than a line apart, and either in the 

 plane of the valves or at right angles to it (leaving round perfo- 

 rations) : it might be called Vioa rectangularis. 



Not uncommon in the schists of Cefn Coch, Glyn Ceiriog, 

 Denbighshire ; in the olive schists of Golden Grove, Llandeilo, 

 Caermarthenshire ; schists of Blain y Cwm W. of Nantyre, Glyn 

 Ceiriog, Denbighshire ; and one doubtful specimen in the sandy 

 schists of the Malverns, Worcestershire. 



{Col. University of Cambridge.) 



Leptcena [Leptagonia] ungula (M'Coy). 



Sp. Char. Semioval ; hinge-line as wide as the shell, forming short, 

 rounded, slightly projecting ears ; cardinal area low, triangu- 

 lar, with a large tubular foramen at the apex of the beak ; re- 

 ceiving valve horse-hoof-shaped from the slope of the deflected 

 front, being at a much more obtuse angle in the middle of the 

 front than at the sides ; visceral disk depressed, very slightly 

 convex towards the beak, rendered rugged by seven or eight 

 concentric wrinkles (only three or four at the margin commonly 

 seen), angle between the disk and the deflected front obtusely 

 rounded, the depth of the latter being rather less than the 

 length of the disk ; entering valve flat, concentrically wrinkled 

 like the receiving one, but with a narrow margin, equally de- 

 flected all round, and only one-fifth or one-sixth the length of 

 the disk; surface of both valves radiated with extremely fine 

 close obtuse punctate striae, about twenty-eight or thirty-two 

 in two lines at four lines from the beak, every 3rd, 5th or 7th 

 of which are usually considerably stronger than the others in 

 all the middle portion ; ii\terior of both valves closely punctured 

 and striate; the close, straight, pallial impressions resemble 

 the external striae on the deflected front, but are only eighteen 

 in the space of two lines ; interior of receiving valve with two 

 rather long, very slightly incurved dental lamellae diverging 

 at 105°, including the rotundato-trigonal pair of muscular 

 impressions which are one-third wider than long, and extend 

 about half the length of the disk, being only separated by a 

 slight indication of mesial septum at their anterior edge ; apex 

 of the triangular boss of the foramen with a small abrupt 

 mucro from the entrance of the matrix into the small tubular 



