ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 929 



Parastrophial (CamarellaX) Salteri (Davidson). 

 (Plate XXII, fig. 42.) 



1868. Rhynchonella Salteri, Davidson, Mon. Brit. Fuss. Brack., vol. iii, pt. vii, p. 188, pi. xxiv, fig. 19 

 (?fig. 20). 

 H907. Camarella Salteri (Davidson), Wirnan, Arkiv f. Zool. (Stockholm), Bd. iii, No. 24, p. 6, t. ii, 

 figs. 4-5. 



Shell subpentagonal, widest across middle. Brachial (?) valve moderately convex ; 

 he;ik obtuse, incurved, somewhat swollen ; shoulders long, about half length of valve, 

 with somewhat flattened slopes forming false areas ; median fold composed of a pair 

 of large angular subparallel plications arising at about one-third the length of the 

 valve and increasing in height and strength to anterior margin ; sides of fold steeply 

 inclined ; lateral portions of shell narrow, smooth, gently convex, without plications. 

 Interior with thin median septum, about one-third the length of valve. 



Dimensions. — Length, 9 mm. ; width, 10 mm. 



Horizon. — " Caradoc " [? Balclatchie Group]. 



Locality. — Penwhapple Glen (Jermyn Street Museum). 



Remarks. — Davidson's description of this species is incorrect, and his figure 

 (op. cit., fig. 19) of the type from Penwhapple Glen is not reliable. The appear- 

 ance of 3 plications on the fold is due to the flattening out of one by crushing, 

 and to an oblique chip broken off its anterior end. It is doubtful if the Boduan 

 specimen (Davidson, op. cit., fig. 20) is referable to the same species. The strength 

 and anterior elevation of the plications, and the presence of only 2, separates the Pen- 

 whapple form from P. Youngi (p. 930), and it is quite distinct from the Ardmillan and 

 Craighead so-called Rh. Salteri (=P. emerita, mihi). It may be a distorted variety 

 of Cam. balclatchiensis, but it cannot be regarded as an altogether satisfactory 

 species, and the precise horizon on which it occurs is somewhat doubtful. 



Parastrophia scotica (Davidson). 

 (Plate XXII, fig. 43.) 

 1883. Rhynchonella scotica, Davidson, Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., p. 201, pi. xi, fig. 26. 



Davidson's figure of the type does not show that out of the 5 plications on 

 the low fold on the brachial valve the 3 middle ones are rather smaller than the 

 outermost ones and are more closely placed together. The outermost plication on 

 each side of the fold is equal in size to the plications on the lateral lobes. In the 

 pedicle-valve there are 4 plications in the sinus. It should also be remarked that 

 the shell is more globose than Davidson showed in his figure. The investigations of 

 Miss Wilson # show that there is much variation in the number of plications on the 

 shell of the allied P. hemiplicata (Hall).f 



In all its essential characters P. scotica much resembles P. hemiplicata (Hall), 



* Wilson, Geol. Surv. Canada Museum, Bull. No. 2(1914), pp. 131-140, pi. iv. 



f Hall, Paleeont. N.Y., vol. i, 1847, p. 144, pi. 33, fig. 10; Hall and Clarke, op. cit, Brach., ii, p. 221, 

 pi. lxiii, figs. 1-3. 



