ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 923 



Genus Porambonites, Pander. 



Porambonites acutiplicata, sp. nov. 



(Plate XXII, figs. 10, 11.) 



Shell subcircular to subelliptical, biconvex, deeply folded ; hinge-line less than 

 width of shell ; cardinal angles obtuse. Pedicle-valve with very deep sharply angular 

 sinus starting from near beak and rapidly deepening and widening to front margin, 

 bounded by sharp angular edges, and with floor produced into acutely pointed tongue, 

 sharply folded along middle line ; beak swollen, rising above hinge-line, incurved 

 (but less so than opposite valve) ; hinge-area steeply inclined, triangular, with median 

 triangular delthyrium. Brachial valve strongly convex, swollen, and inflated, with 

 high rounded fold corresponding to sinus occupying middle third of valve on anterior 

 margin, which is acutely emarginate ; lateral lobes gently convex, not strongly 

 marked off from fold ; beak large, high, swollen, incurved, rising above beak of 

 opposite valve, with vertical triangular hinge-area lying in plane of valve. Surface 

 of shell ornamented with small closely set circular pits in radial lines, about ten radial 

 lines to every 4 mm., and about ten pits of a row in every 3 mm. 

 Dimensions.— 



Length . ... 



Width 



Depth 



Horizon. — Stinchar Limestone Group. 

 Locality. — Craighead. 



Remarks. — There are only two specimens of this interesting shell in Mrs Gray's 

 collection, and neither show the internal characters. It is quite distinct from 

 Porambonites intercedens, var. Jilosa, M'Coy, of Co. Waterford, # and from those 

 described by Davidson from Wrae Quarry, t which have a broad flat sinus. In re- 

 ferring to the valve carrying the fold as the brachial valve I have followed Noetling4 



Genus Camarella, Billings. 



Camarella balclatchiensis, (Davidson). 



(Plate XXII, figs. 12-15.) 



1883. Rhynchonella balcletchiensis, Davidson (pars), Man. Brit. Foss. Brack., vol. v, Silur. Suppl., 



p. 160, pi. x, fig. 15 (non fig. 16, nee pi. xi, fig. 23). 

 1883. Rhynchonella xmula, Salter, Davidson (pars), ibid., p. 160 (non pi. x, fig. 17). 



Shell subtriangular to subpentagonal, broadest anteriorly, rounded at sides, 

 usually as wide as long or rather wider than long, biconvex. Pedicle-valve with 

 median sinus commencing at from one-third to one-half the length of the valve, 

 increasing rapidly in width to anterior margin to more than one-third the anterior 



* Davidson, op. cit., vol. iii, p. 195, pi. xxv, fig. 16 ; pi. xxvi, figs. 1, 2. 

 t Davidson, ibid., pi. xxv, figs. 1 7-19 ; pi. xxvi, fig. 3. 

 J Noetling, Zeitschr. deut. geol. Gesellsch., Bd. xxxv, 1883, p. 535. 

 TRANS. ROY. SOC. EDIN., VOL. LI, PART IV (NO. 26) 132 



(1) 



(2) (Crushed specimen.) 



18 



? 20 mm. 



18 



24 mm. 



16 



16 mm. 



