ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 909 



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



Localities. — (l) Minuntion, Craighead ; (2) Balclatchie. 



Remarks. — It is difficult to understand the reasons which led Davidson to 

 include this well-marked shell in his Rhynchonella balclatchiensis (see p. 923), for 

 it is more transverse and more convex, the fold and sinus are much stronger and 

 more angular ; there is no short groove in the middle of the anterior end of the 

 fold, and there are more or less distinct radial lines on the lateral lobes. A 

 comparison with Davidson's type-specimens of Rh. [Camarella] balclatchiensis 

 proves that their association is inadmissible. Our shell is more like T. extans, 

 Emmons,* and it also resembles Mimulus contrarius, Barrande,t and M. ivaldron- 

 ensis, Miller and Dyer,| but the two latter occur in the Silurian. It differs from 

 T. nucleoides, sp. nov. (see below), of the Stinchar Limestone, in its more transverse 

 shape, flatter pedicle-valve, and the more angular fold on the brachial valve, as 

 well as in its ornamentation. In general shape it bears a superficial resemblance 

 to Pugnax acuminata (Martin) of the Carboniferous. 



Triplecia insularis (Eichwald). 



1842. Terebratula insularis, Eichwald, Urwelt. Russl., vol. ii, p. 49, pi. ii, figs. 6a-c. 

 1870- Orthis insularis, Eichwald, Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 273, pi. xxxvii, 

 figs. 8-15. 



Davidson does not record this species from Girvan, but there are good examples 

 from the Starfish Bed and Whitehouse Beds, showing the characteristic external 

 features and the peculiar muscle-scars, etc., in internal casts. Some of these from 

 Shalloch Mill were labelled by Davidson Porambonites intercedens, Pander, with a 

 query ; but they neither show the external ornamentation of that species nor its 

 other characters. The form of Tr. insularis occurring in these Girvan localities is 

 subovaLin shape and rarely transverse, and those from the Starfish Bed especially 

 resemble the specimen from the Chair of Kildare figured by Davidson (op. cit., iii, 

 pi. xxxvii, figs. 8, 12, 13, 14) and the shell named Orthis galea, M'Coy,§ from the 

 same locality and horizon. 



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



Localities.— (I) Shalloch Mill ; (2) Thraive Glen. 



Triplecia ? nucleoides, sp. nov. 



(Plate XX, figs. 6, 7.) 



Shell subtriangular, rounded to subcircular, widest a little in front of middle, 

 strongly biconvex, inflated ; anterior margin strongly sinuated ; hinge-line about 

 one-third the width of shell. Pedicle-valve with wide rounded sinus arising at half 

 the length of valve, rapidly widening to more than one-third the width of valve on 



* Hall and Clarke, op. cit., Brach., i, p. 269, pi. xic, figs. 1-7. 



t Barrande, Syst. Silur. Boheme, vol v, pi. ix, figs, via, e. 



X Hall and Clarke, op. cit., pi. xic, figs. 23-28. § M'Coy, Syn. Silur. Foss. Irel., p. 30, pi. iii, fig. 12. 



