ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 941 



on the fold, and it is rather more transverse in shape ; but it seems doubtfully 

 separable, and the material is very poor. 



Rhynchotrema sp. 

 (Plate XXIV, fig. 7.) 



There is one pedicle-valve of a rhynchonelloid from the Balclatchie conglomerate 

 in Mrs Gray's collection which may be compared with Winchell's Rhynchotrema 

 Ainsliei # from the Trenton Shales. It has 5 regular equal ribs in the shallow sinus, 

 which rapidly widens anteriorly, and 7-8 ribs on each lateral lobe, gradually 

 decreasing in size to the cardinal edges. The two small subparallel dental plates, 

 about one-sixth the length of the valve, are well seen. The number of ribs at once 

 separates it from Rh. Lapivorthi and Rh. girvanense. 



Dimensions. — Length, 16 mm. ; width, 17-18 mm. 



Horizon. — Balclatchie Group. 



Locality. — Balclatchie (conglomerate). 



Genus Rhynchotreta, Hall. 



Rhynchotreta ardmillanensis (Davidson, MS.). 



(Plate XXIV, figs. 8-17.) 



? 1883. Rhynchonella cuneata, Dalman % Davidson (pars), Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., 

 p. 152, pi. x, figs. 9, 9a, 9b, non fig. 10 (nou Rh. cuneata, Davidson, op. cit., vol. iii, p. 164, 

 pi. xxi, figs. 7-11). 

 1 1883. Rhynchonella Weaveril, ibid., p. 158, pi. x, fig. 24. 

 Non 1868. Rhynchonella Weaveri, Davidson, op. cit., vol. iii, p. 185, pi. xxiv, fig. 14. 



Shell cuneiform, subtrigonal, longer than wide, broadest and subtruncate 

 anteriorly, gently biconvex, somewhat flattened, without fold or sinus (or only 

 weak traces of them) ; long sloping shoulders with elongated more or less flattened 

 and excavated false areas which extend three-fourths to four-fifths the length of the 

 shell. Pedicle-valve gently convex, with rarely very weak broad shallow sinus 

 or undulation in front margin ; beak high, pointed, acute, slightly incurved, per- 

 forated by small foramen ; interior with two thin subparallel long vertical dental 

 plates. Brachial valve gently convex, less so than opposite valve, sometimes 

 flattened or with slightly increased median convexity but no definite fold ; beak 

 small, pointed, lower, less acute and less prominent than in opposite valve, scarcely 

 incurved ; interior with minute spondylium and single long straight median septum 

 extending nearly half the length of the valve. Surface of both valves covered with 

 14-18 small low subangular or rounded equal plications, strongest near front margin, 

 and all straight except outermost lateral ones, which curve back very slightly. 



Dimensions. — Length (average), 7-9 mm. ; width (average), 5-8 mm. 



* Winchell and Schuchert, Palxont. Miunes., vol. iii, p. 459, pi. xxxiv, figs. 1-8. 



