ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 805 



tudinal median ridge more than half length of shell ; pair of strong oval, rather 

 deep, slightly oblique contiguous muscle-scars situated a short distance in front of 

 beak. Surface of shell with very fine concentric lines and thin undulated irregular 

 lamellae ; internal layer with very delicate and closely placed radial striae. 



Dimensions. — Length (estimated) about 30 mm. ; maximum width about 21 mm. 



Horizon. — Ballantrae Group. 



Locality. — Bennane Head, Ballantrae. 



Remarks. — Only one specimen of this shell in the Survey Museum at Edinburgh 

 (Reg. No. 174) is known to me, and it has the anterior part broken and imperfect. 

 Its shape, however, is very distinctive, and it somewhat resembles in this respect 

 L. cuneata, Conrad,* from the Medina Sandstone. The muscle-scars seem to be like 

 those in L. Davidsoni, Barrande,t from Stage Dd. 4. The Silurian species L. crumena, 

 Phillips,| nas somewhat the same shape. 



Lingula Lewisi, Sowerby. 



1839. Lingula Leioisi, Sowerby, in Murchison's Silur. Syst., p. 615, pi. vi, fig. 9. 



1866. Lingula Lewisi, Sowerby, Davidson, Mon. Brit. Foss. Brach., vol. iii, p. 35, pi. iii, figs. 1-6. 



This species is represented at Mulloch Hill and Craigens. The oblong siibquadrate 

 shape distinguishes it from the other Silurian species in the G-irvan district, and 

 though Davidson does not record it from this area, and doubts § the reported occur- 

 rence of this species in Llandovery beds (as it is typically a Ludlow form), it does not 

 seem possible to distinguish these Mulloch Hill and Craigens specimens from the 

 Ludlow types. In size these Mulloch Hill shells measure about 13 mm. long by 

 10 mm. wide. 



Horizons. — (l) Mulloch Hill Group ; (2) Saugh Hill Group. 



Localities. — (l) Mulloch Hill; (2) Craigens. 



Lingula mediostriata, sp. nov. 



(Plate II, figs. 15, 16.) 



1 1883. Lingula ovata, Davidson, Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., p. 207, pi. xvii, fig. 25. 



Shell ovate to sub-oblong •; sides subparallel, very slightly arched ; anterior end 

 obtusely rounded to subtruncate ; biconvex, somewhat flattened anteriorly. Pedicle- 

 valve gently convex ; beak pointed, with short shoulders diverging at 75°-90° and 

 reaching less than one-third the length of shell. Brachial valve with inconspicuous 

 obtuse beak and with shoulders diverging at very wide angle. Surface of valves marked 

 by numerous closely placed minutely undulated fine concentric lines with occasional 

 stronger growth-ridges, and a median group of very delicate straight radiating lines 



* Hall and Clarke, op. cit., Brach., i, p. 12, pi. i, figs. 11, 12. 



t Barrande, Syst. Silur. Boheme, vol. v, 1879, pi. civ, figs, viii, 1-4. 



| Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, pi. ii, fig. 3. ' 



§ Ibid., p. 35. 



