894 1>R F. i;. C. REED ON THE 



smaller development of the transverse pits and rugee in the interspaces. The 

 true type of Str. corrugatella is Portlock's Orthis corrugata from the Bala of 

 Desertcreat, which Davidson refigurecL* Our shell is more allied to Stropheodonta 

 corrugata, Conrad, f from the Clinton Beds, and perhaps to Stroph. sculpta, Gagel,} 

 and especially in ornamentation to Stroph. Patersoni, Hall.§ This new species is 

 named after Robert Jameson the Professor. of Natural History in Edinburgh at 

 the end of the eighteenth century. 



Subgenus leptostrophia, Hall and Clarke. 

 Stropheodonta (Leptostrophia) Jilosa (Sowerby), var. nov. mullochensis. 



(Plate XVII, figs. 4-8.) 



L883. Strophomena expa?isa, Sowerby, Davidson, Man. Brit. Foss. Brack., vol. v, Silur. SuppL, p. 194, 

 pi. xv, figs. 1, 3-5 (non fig. 2). 



Shell subquadrate to semielliptical ; much compressed, plano-convex ; hinge-line 

 equal to width of shell ; cardinal angles rectangular, rarely obtuse. Pedicle-valve 

 very gently convex, flattened in cardinal region laterally ; beak small, acute, scarcely 

 projecting above hinge-line ; hinge-area narrow, linear ; hinge-line with short marginal 

 denticulations for whole length. Interior of pedicle-valve with thin long linear 

 dental plates diverging at about 60° to hinge-line ; muscle-scar triangular, composed 

 of pair of weakly impressed flabelliform diductors, undefined in front, enclosing 

 elongated oval adductor scar. Brachial valve flat ; hinge-area narrow, linear, sub- 

 equal to that on pedicle-valve ; beak small, inconspicuous. Interior of brachial valve 

 with small bilobate cardinal process, the narrow elongate lobes diverging anteriorly 

 at about 30° ; crural plates short, blunt, diverging at about 45° to hinge-line ; adductor 

 scars very faint, with low broad median ridge between them. Surface of valves 

 ornamented with very numerous fine subequal delicate radii curving back a little on 

 each side and increasing by frequent intercalation ; every fifth or sixth radius is 

 rather stronger, and a few of these are primaries, continuous from beak to margin. 

 Shell densely punctate with small pits, equal and equidistant and closely set between 

 the radial lines. A. few small short bent concentric rugse occasionally developed on 

 each side of beak close to hinge-line, and meeting it at acute i ngles. 



Dimensions. — 



(1) (2) 



Length . . . . . .18 23 mm. 



Width 22 34 mm. 



Horizon. — Mulloch Hill Group. 



Localities. — Mulloch Hill, Craigens. 



Remarks. — It is curious that this shell should have been mistaken for Raf. 



* Davidson, op. cit., vol. iii, pi. xli, fig. 8. 



t Hall, Palxont. N.Y., ii, 1852, pi. 21, figs. 2o^2c ; Grab.vu, Bull. New York State Mm., No. 45, vol. ix (1901J 

 p. 181, fig. 85. 



I Gagkl, op. cit., p. 46, t. iii, Bg. 21. 5; Hall and Clakke, Brach., i, pi. xiv, rig. 16. 



