930 DR F. R. C. REED ON THE 



from the Trenton Limestone, and also is much like the Swedish " Camerella" 

 Tornquisti, Wiman.* Hall and Clarke t recognised that Davidson's Rh. scotica 

 belonged to Parastrophia. 



Horizon.— Stinchar Limestone Group. 



Locality. — Craighead. 



Parastrophia thraivensis, sp. nov. 

 (Plate XXII, figs. 44, 45.) 



Shell strongly biconvex, with deeply re-entrant valves, subcircular ; beaks low, 

 obtuse, approximate. Pedicle-valve with deep sinus increasing in width and depth 

 anteriorly, with sharp prominent angular edges, and with flattened floor produced into 

 blunt tongue, and bearing in anterior half 2 small closely placed plications of equal 

 size ; sides of sinus steep, high ; lateral lobes of valve bearing 3-4 coarse subangular 

 plications arising at about half the length of valve, those bordering the sinus 

 being the longest, sharpest, and most prominent. Interior of pedicle-valve with 

 short narrow spondylium and median septum extending from it about one-third the 

 length of valve. 



Brachial valve strongly convex, with median fold composed of a pair of broader 

 lateral subangular plications and a smaller narrower median one, all continuous from 

 beak to margin and subparallel ; lateral lobes with 3-4 lower plications shorter and 

 arising nearer margin. Surface of shell marked by few strong concentric growth- 

 ridges. 



Dimensions. — 



Length .... 



Width 



Horizon. — Drummuck Group (Starfish Bed). 

 Locality. — Thraive Glen. 



Remarks. — This shell is very closely allied to " Camerella" angulosa, Tornquist, J 

 from the Leptsena Limestone. Parastrophia reversa (Billings) § also bears a con- 

 siderable resemblance to it. 



Parastrophia Youngi, sp. nov. 



(Plate XXII, figs. 46, 47.) 



Shell more or less globose, subcircular ; beaks approximate, subequal, swollen, 

 obtuse. Pedicle-valve convex, with broad shallow median sinus arising at some 

 distance from beak, with flattened floor continued as obtuse tongue bent down and 



* Wiman, Bull. Geol. Instit. Upsala, No. 10, vol. v, pt. ii, 1900, p. 175, pi. vii, figs. 22-25. 



(• Hall and Clarke, op. cit., Brack, ii, p. 223. 



| Lindstrom, Fragm. Sihir., p. 23, pi. xiii, figs. 14-19. 



§ Hall and Clarke, op. cit., Brack, ii, pi. lxiii, figs. 8-14. 



(1) 



(2) 



10*5 



9*0 mm. 



10'0 



10'5 mm. 



