ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 895 



expansa; the denticulations of the hinge-line can usually be observed in all the 

 examples, and are distinct in one of those figured by Davidson. A comparison with 

 the well-known Wenlock species Str. filosa (Sowerby)* shows that the Girvan form 

 can only be separated as a variety, differing by the absence of angular mucronate 

 wings to the cardinal angles, and by its more subquadrate shape. The Llandovery 

 species Str. compressa (Sowerby) f resembles the Girvan shell more closely in out- 

 line, but less closely in its internal characters. 



Stroplieodonta (Leptostrophia) subfilosa, sp. nov. 

 (Plate XVII, figs. 9-12.) 

 Shell semielliptical, widest along hinge-line, much compressed, flattened to plano- 

 convex ; cardinal angles subrectangular ; hinge-line furnished with regular small denti- 

 culations along its whole length. Pedicle-valve fiat, or very slightly convex ; beak 

 small, scarcely rising above hinge-line ; hinge-area narrow, triangular, longitudinally 

 striated, nearly at right angles to plane of valve, with small triangular delthyrium 

 and deltidium ; interior of pedicle-valve with pair of small teeth and flabelliform 

 divergent diductor scars, anteriorly truncated, extending about two-fifths the length 

 of the shell and embracing moderately broad oval adductor scars between them. 

 Brachial valve slightly concave or nearly flat ; beak inconspicuous, not raised ; hinge- 

 area very narrow, nearly at right angles to valve. Surface of valves ornamented 

 with about 30-40 straight thread-like radii, of which about half the number are 

 primaries, the others arising as secondaries or tertiaries at about half to three-fourths 

 the length of the valve, all subequidistant and fairly regularly developed ; interspaces 

 rather wide, holding 3-5 delicate radial striae crossed by fine concentric striation. 

 Dimensions. — 



(1) (2) 



Length 16 13'5 mm. 



Width 23 20*0 mm. 



Horizon. — Stinchar Limestone Group. 



Locality. — Craighead. 



Remarks. — The denticulation of the hinge-line and flatness of the shell obliges 

 us to separate this from Rafinesquina, but the ornamentation is much like that of 

 R. expansa, var. Macallumi. The flatness and small depth of the shell do not seem 

 due to compression in the rock. The muscle-scars, so far as they are known, support 

 the reference to Stropheodonta, but no interior of a brachial valve has been observed. 

 The species seems allied to Stroph. compressa, Sow.,} and Stroph. filosa,l Sow., but 

 these are both Silurian species. The hinge-line of the pedicle-valve has a series of 

 small separated pits sunk in the thickness of the shell to receive corresponding small 

 teeth of the opposite valve, and such is the case in Stroph. filosa. 



* Sowerby, in Murchison's Silurian System, p. 630, pl. xiii, fig. 12 ; Davidson, op. cil, vol. iii, pt. vii, p. 307, 

 pi. xliv, figs. 14-20. + /MA> p 315; pl xlvi) figs 7 ._ 10 



| Davidson, op. cit, vol. ili, p. 315, pl. xlvi, figs. 7-10. § Ibid., p. 307, pl. xliv figs. 14-20. 



