892 DR F. R. C. REED ON THE 



over the surface as in the type form from Ireland. The fact that the radii are straight 

 at once distinguishes it from Str. Jamesoni (see p. 893), in which they are curved. 



In these Girvan examples ' of Str. corrugatella the cardinal process is occasionally 

 preserved, and we note that it is high, strongly bilobed, and rerlexed, being composed 

 of two large oval lobes divergent posteriorly ; the crura are far apart, short, and 

 inclined at about 45° to the hinge-line. In the pedicle-valve the teeth are very 

 short ; the muscle-scar is rather small, subcircular, and composed of two feebly 

 impressed radially grooved contiguous flabelliform diductors. On each side of the 

 beak the line transverse denticulations along the whole length of the hinge-line can 

 be observed. The supposed Shalloch Mill examples are poor and doubtful. 



Dimensions. — Length, 20 mm. ; width, 30 mm. 



Horizons. — (l) Drummuck Group (Starfish Bed) ; (2) Whitehouse Group? 



Localities.— (l) Thraive Glen ; (2) Shalloch Mill. 



Stropheodonta donax, sp. nov. 

 (Plate XVI, figs. 21-27.) 



Shell transversely semicircular to semielliptical, fully twice as wide as long, sub- 

 auriculate, widest along hinge-line, concavo-convex to plano-convex, compressed ; 

 hinge-line very minutely denticulated ; cardinal angles subacute, less than right 

 angles, somewhat produced. Pedicle-valve gently convex; beak small, slightly 

 rising above hinge-line, gently incurved ; hinge-area narrow, elongate-triangular, 

 lying in plane of valve ; teeth small, short ; muscular area small, transversely sub- 

 circular to subpentagonal, well defined, with sharp raised margins about one-fourth 

 to one-third length of valve ; diductors short, subtriangular", embracing laterally 

 narrow lanceolate elongated adductor scars produced in front of diductors and 

 separated by median ridge, sometimes continued weakly in front of scars. Brachial 

 valve concave to flat ; beak inconspicuous ; hinge-area steeply inclined to plane of 

 valve, narrower than in opposite valve ; cardinal process divided to base into two 

 parallel and closely placed stout lobes, with posterior faces grooved ; crural plates 

 low, short, widely divergent, inclined at about 20° to hinge-line. Surface of val 

 covered with numerous closely placed small subequal regular rounded riblets, in- 

 creasing by intercalation to 100-130 on margin, separated by interspaces equal in width 

 to riblets, with fine concentric striation and a few stronger growth-ridges over all 



Dimensions. — Length, 15-16 mm. ; width, 28-31 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Remarks. — The denticulations on the hinge-line are very minute, and may easily 

 escape notice, as this part of the shell is generally imperfectly preserved. But the 

 examination of a large series of specimens has proved their existence, and they 

 appear to extend the whole length of the hinge-line. A good internal cast of a pedicle 



