912 DR F. R. C. REED ON THE 



free triangular projections ; these Davidson called the dental plates, but it is doubtful 

 if they are homologous with true dental plates, as they seem to be within the cavity 

 of the beak and away from the teeth. These plates project into the base of the 

 short flabelliform muscle-scars (? diductors) which are in contact in the middle line 

 and form a triangular transverse scar about one-third the length of the valve ; the scars 

 are separated by a narrow groove, and each scar is also longitudinally divided into 

 two subequal portions. A pair of narrow short obscure adductors (?) lies immediately 

 in front of them. 



The brachial valve has a low inconspicuous beak, and is marked anteriorly (or for 

 most of its length) by a wide indefinite shallow sinus, having a broad rounded anterior 

 tongue bending up into the marginal fold on the opposite valve. The interior of 

 the brachial valve is unknown. With these corrections and additions, Davidson's 

 description holds good. 



This species may be compared with Rhynchonella apiculata, Salter and Forbes 

 MS., # from the Chair of Kildare. The fold being in the pedicle-valve and the 

 sinus in the brachial recalls Mimulus perversus, Barrande,t the type of the 

 genus Mimulus, rather than any species of Triplecia, and it seems more probably 

 to belong to Mimulus than to any other genus. 



Horizons.- — (l) Penkill Group ; (2) Camregan Group ; (3) Saugh Hill Group ? 



Localities. — Penkill, Penwhapple Glen ; (3) Bargany Pond Burn ; (3) Wood- 

 land Point. 



Genus Streptis, Davidson. 

 Streptis Hornei, sp. nov. 



(Plate XX, figs. 24, 25.) 



1883. Triplegia monilifera, Davidson (pars), Man. Brit. Foss. Brack., vol. v, Silur. Stippl., p. 147, 

 pi. viii, fig. 31 j p. 225. 

 Non 1870. Triplesia monilifera, Davidson, op. cit., vol. iii, p. 200, pi. xxv, figs. 3-5. 



Shell small, transversely elliptical, symmetrical, biconvex ; hinge-line less than 

 maximum width of shell ; cardinal angles rounded. Pedicle-valve moderately 

 convex, with broad shallow median sinus widening anteriorly, with rather sharp 

 edges defining it laterally ; beak small, acute ; hinge-area triangular. Brachial valve 

 more convex, with regular median rounded fold extending from beak to margin, 

 widening anteriorly ; beak rounded, incurved, inconspicuous. Interior of pedicle- 

 valve with pair of thin divergent dental plates following the marginal ridges of the 

 sinus and extending about one-third the length of valve. Surface of shell marked 

 with 8-9- concentric sharp lamellae, having regularly frilled edges, not nodulated; 

 interspaces with fine concentric lines. 



* Davidson, op. cit., vol. iii, p. 202, pi. xxv, fig. 6. 



t Barrande, Syst. Silur. Boheme, v, pi. i, fig. 3, C, E ; Hall and Clarke, op. cit., Brach., i, p. 272, pi. xic, 

 figs. 31, 32. 



