ORDOVTCIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 803 



Genus Lingula, Bruguiere. 

 Lingula amabilis, sp. nov. 



(Plate II, figs. 3-8.) 



1866. Ling/da attenuata, Sowerby, Davidson (pars), Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 44, 



pi. iii, figs. 24, 25 (non cet.). 

 1883. Lingula attenuata, Sowerby, Davidson (pars), op. cit., vol. v, Silur. Suppl., p. 206, pi. xvii, 



figs. 13-15 (non cet.). 



Shell sub-ovate to subcuneiform, widest near anterior end, obtusely rounded in 

 front, weakly biconvex. Pedicle-valve with acutely pointed somewhat produced 

 beak ; shoulders long, sloping away at about 60° to 75°, passing gradually into 

 arched sides. Brachial valve obovate, with inconspicuous beak; interior with weak 

 median septum extending about half the length of valve. Interior of both valves 

 marked with widely spaced irregularly distributed coarse pits, and strong concrete 

 lateral muscle-scars (occasionally visible). Surface of valves covered with fine con- 

 centric lines and growth-ridges of somewhat unequal strength. 



Dimensions. — 



Pedicle-valve. Brachial valve. 



(1) Balclatchie. (2) Ardmillan. (3) Balclatchie. 



Length .... 10"4 mm. 17'0 mm. 9'2 mm. 



Maximum width . . 8'0 mm. 12'0 mm. 7'1 mm. 



Horizon. — Balclatchie Group. 



Localities. — Balclatchie, Ardmillan. 



Remarks. — It is doubtful if this shell should be regarded as only a variety of 

 Lingula attenuata, Sowerby, * rather than as a distinct species. The types of 

 Sowerby's shell came from the Llandeilo Flags of Rorington and Meadowtown and 

 are poor, and the description, as is frequently the case in older works on Silurian 

 brachiopods, is inadequate. Davidson's figures of the Girvan shells, which he 

 attributes to L. attenuata, make the shoulders appear too long and the sides too 

 short in the pedicle- valves. 



Lingula brevis, Portlock, var. nov. angustior. 

 (Plate II, figs. 9, 10.) 



?1843. Lingula brevis, Portlock, Geol. Rep. Londond., p. 443, pi. xxxii, fig. 2. 

 Non 1883. Lingula brevis, Portlock, Davidson, Mon. Brit. Foss. Braeh., vol. v, Silur. Suppl., pi. xvii, figs. 

 27-30, 36. 



In certain shells from the Balclatchie Group which bear a resemblance in many 

 ways to Lingula brevis, Portlock, there are a few points of difference which suggest 

 that they should be separated as a variety or perhaps as a distinct species. The beak 



* Sowerby in Murchison's Silur. Syst., 1839, p. 641, pi. xxii, fig. 13. 

 TRANS. ROY. SOC. EDIN., VOL. LI, PART IV (NO. 26). 117 



