ORDOVICTAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 927 



Camarella Thomsoni (Davidson). 



(Plate XXII, figs. 29-32.) 



1868. Rhynchonella Thomsoni, Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 186, 



pi. xxiv, fig. 18. 

 1883. Rhynchonella Thomsoni, ibid., vol. v, Silur. Suppl., pp. 148, 225. 



The presence of 2-3 marginal plications in the sinus of the pedicle-valve, the 

 broad low fold with 2-3 plications on it in the brachial valve, the presence of lateral 

 plications, and the absence of such sharp well-defined edges to the sinus help to 

 distinguish it from C. balclatchiensis, but it is a variable species. In the more 

 transverse varieties with accentuated fold and sinus we see a resemblance to 

 C. Peachi, and the flattened more elongated examples are difficult to distinguish 

 from the Craighead variety of C. cuneatella. Davidson's type of the species 

 C. Thomsoni was found at Craighead. The internal characters are unfortunately 

 unknown. The more transverse swollen shells may possibly be the adult shells, 

 and the flatter, more triangular ones, like Davidson's figured one, may be immature 

 individuals. The frequent want of symmetry in the development of the plications 

 is noticeable in this and allied species. 



Horizon. — Stinchar Limestone Group. 



Locality. — Craighead. 



Genus Parastrophia, Hall and Clarke. 

 Parastrophia emerita, sp. no v. 



(Plate XXII, figs. 33, 34.) 



1883. Rhynchonella Salteri, Davidson (pars), Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 225. 

 Nonl868. Rhynchonella Salteri, Davidson, ibid., vol. iii, pt. vii, p. 188, pi. xxiv, figs. 19, 20. 



Shell transversely subpentagonal. Brachial valve moderately convex, with broad 

 low median fold arising in anterior half with elevated edges and somewhat depressed 

 centre ; fold composed of 4 plications consisting of a pair of closely placed small 

 short median ones only developed near the margin, and a pair of considerably larger 

 more elevated longer subangular lateral ones, tending to divide into 2 smaller ones 

 near their anterior extremities. Lateral lobes separated from fold by wide deep groove 

 on each side, and with traces of 2-3 weak low rounded almost obsolete plications 

 near the margins. Interior of brachial valve with minute spondylium and straight 

 median septum nearly half the length of the valve. Surface of shell ornamented 

 with a few concentric lamellose growth -ridges and lines. 



Dimensions. — Length, 8 mm ; width, 10'5 mm. 



Horizons. — (l) Stinchar Limestone Group; (2) Balclatchie Group. 



Localities. — (l) Craighead ; (2) Ardmillan Brae. 



Remarks. — These small shells were labelled by Davidson Rhynchonella Salteri* 



* Davidson, op. cit., iii, p. 188, pi. xxiv, figs. 19, 20. 



