ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 925 



here described and restricted (see p. 927), but the former differs in the fold being 

 composed of a pair of plications and in the broader outline of the shell ; but the 

 separation of young or imperfect specimens is difficult. 



C. Volborihi (Billings),* the type of the genus, is more closely allied, and may be 

 identical ; it is a typical Trenton form. Our specimens of C. balclatchiensis do not 

 clearly show the spondylium, owing to their imperfect preservation, but otherwise 

 agree in all essential characters. 



Camarella balclatchiensis (Davidson), var. 



(Plate XXII, figs. 16-18.) 



1883. Rhynchonella balcletchiensis, Davidson (pars), Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., 

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

 1 1883. Rhi/nchonella portlockiana, Davidson (pars), ibid., p. 159, pi. x, fig. 12 (non figs. 13, 14). 

 Non 1868. Rhynchonella ? portlockiana, Davidson, ibid., vol. iii, pt. vii, p. 189, pi. xxiv, figs. 23-25. 



This variety is longer, and more elongated than the type ; it is widest across 

 the middle instead of anteriorly, and is subpentagonal in shape, with longer sloping 

 shoulders which meet at the beak of the pedicle-valve at about 45°-50°. In these 

 respects it differs from the Craighead type. The median plication in the sinus 

 of the pedicle-valve always seems to be obsolete and the fold in the opposite valve 

 may be ungrooved, but the specimens are poorly preserved and not satisfactory, 

 so that a distinctive name is not applied to them. 



Horizon. — Balclatchie Group (conglomerate). 



Locality. — Balclatchie. 



Cam.arella ? Conybearei, sp. nov. 

 (Plate XXII, figs. 19-24.) 



Shell small, elongate, oval to subtrigonal, posteriorly pointed, anteriorly rounded, 

 with long sloping shoulders more than half the length of shell ; anterior margins of 

 valves meeting in deep zigzag junction. Pedicle-valve with small beak acutely 

 pointed at about 30° ; surface of valve occupied by two pairs of large rounded or 

 subangular nearly equidistant plications, the middle pair larger than the lateral 

 pair (but all continuous from beak to margin). Brachial valve with smaller lower 

 more obtuse beak than in opposite valve ; surface occupied by a median rounded 

 plication arising in front of beak, and a pair of larger more elevated lateral plications 

 similar to those on other valve and continuous from . beak to margin. General 

 surface of both valves marked by regular rather sublamellose concentric striae. 



Dimensions. — -Length, 4-5 mm. ; width, 2 '5-3 "5 mm. 



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



Localities. — (l) Balclatchie (conglomerate) ; (2) Craighead. 



Remarks. — This small shell was simply labelled ' Rhynchonella ' sp." by 



* Billings, Genl. Canada, 1863, p. 143, fig. 77 ; Hall and Clarke, op. cit., Brach., ii, p. 220, pi. lxii, figs. 11-18. 



