ORDOVIOIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 949 



rather higher and more inflated, and this whole valve is more swollen. Internally 

 also there are some differences, and the figures of the interior of pedicle-valves from 

 Drummuck given by Davidson are inaccurate, for the strongly marked short flabelli- 

 form muscle-scars on each side of and slightly behind the crescentic median callosity 

 were not shown, nor was the thickening of the shell inside the beak clearly indicated. 

 In the brachial valve there is also a strong median septum proceeding from the small 

 thickened hinge-plate, and extending from one-fourth to three-fourths the length of 

 the valve ; the crura are short and rod-like, and there are two pairs of faintly marked 

 elongate adductors. These differences are sufficient to separate off our Drummuck 

 shell as a variety. The Whitehouse specimens are less satisfactorily preserved and 

 seem more like the Welsh form. 



I do not think that there is a " shoe-lifter " process in the pedicle-valve, as David- 

 son represents in his restorations of the interior, and our shell seems rather to possess 

 the internal characters of Dayia navicula (Sow.) # than of Merista, sens. restr.,f 

 for the median crescentic thickening in the floor of the valve has merely its anterior 

 face slightly excavated, and it thins off on each side into lateral horns. 



Probably the Keisley species Dayia pentagonalis, Reed,| is closely allied to the 

 Drummuck form. 



Horizons. — (l) Drummuck Group (Starfish Bed) ; (2) Whitehouse Group. 



Localities. — (l) Thraive Glen ; (2) Whitehouse Bay, Shalloch Mill. 



Dayia, sp. ind. 

 (Plate XXIV, fig. 36.) 



Some small subcircular shells from Bargany Pond Burn seem to possess the 

 internal characters of Dayia and resemble D. cymbula rather than the Silurian 

 D. navicula (Sow.). The material is, however, too poor for a satisfactory identifica- 

 tion. Davidson labelled them Merista cymbula. 



Dimensions. — Width, 3'5-4'0 mm. 



Horizon.— Camregan Group. 



Locality. — Bargany Pond Burn. 



Genus Cyclospira, Hall and Clarke. 



The occurrence of this genus in the Girvan area rests on doubtful evidence. The 

 type chosen by Hall and Clarke is Orthis bisulcata, Emmons, § of the Trenton 

 Limestone. Externally this shell is very similar to Dayia navicula (Sow.) of the 

 Wenlock and Ludlow Beds, but internally it differs essentially. 



* Davidson, op. cit., vol. iii, p. 190, pi. xxii, figs. 20-23 ; ibid., vol. v, Silur. Suppl, p. 96, pi. v, figs. 1-4. 

 + Hall and Clarke, op. cit, Brach., ii, p. 70. 



I Reed, Quart. Jo urn. Geol. Soc, vol. liii, 1897, p. 75, pi. vi, figs. 5, ba-c. 



§ Emmons, Geol. New York, Rep. 2nd Distr., 1842, p. 395, fig. 4 ; Hall and Clarke, op. cit., Brach., ii, p. 146, 

 pi. liv, figs. 38-40. 



