GASTEROPOD FAUNA IN THE MILLSTONE GRIT OF SCOTLAND. 343 



with this species at Pule Hill, and I have recognised that species in a collection from 

 Garngad Road made by Mr J. Neilson of Glasgow. 



Locality. — 9 to 10 feet above the Castlecary Limestone, Torwood, Stirlingshire; 

 Greenfoot Quarry, near Gain Farm, Dumbartonshire ; and Bilston Burn, Midlothian. 



Nucula gibbotsa, Flem., vide Hind, Pal. Soc, 1897, Brit. Garb. LamelL, p. 178. PI. I. 



figs. 18, 19. 

 Nuculana attenuata, Flem., sp., vide Hind, Pal. Soc, 1897, Brit. Garb. Lamell., p. 195. 

 Ctenodonta Ixvirostris, Portl., sp., vide Hind, Pal. Soc, Brit. Garb. Lamell., pp. 183, 210; pt. ii. 



p. 164. 



These three species occur together at many horizons in the Carboniferous sequence, 

 from the Calciferous Sandstone series to the Coal Measures. 



It is interesting to note that each genus is represented in the Coal Measures of 

 North America by a closely allied species — Nuculana (Yoldia) subsulcata, Nuculana 

 bellistriata, Ctenodonta (allorisma) reflexa. 



Nuculana Isevistriata, Meek and Worthen, sp. (PI. I. fig. 17.) 

 For synonymy, vide Hind, Pal. Soc, 1897, Brit. Garb. Lamell., p. 205. 



This species is found in the St Louis group of the Lower Carboniferous beds of 

 North America, but in Scotland it is very common at Waulkmill Glen in the Upper 

 Limestone series. It seems to be rare in the Millstone Grit localities. 



Locality. — River Avon, between the outcrop of the Castlecary Limestone and the 

 Railway Viaduct. 



Modiola subelliptica, Meek, 1867. (PI. I. fig. 20.) 



Clidophorus (Pleurophorus) occidentalis, Geinitz, 1866, Garb, und Dyas in Nebraska, p. 23, pi. ii. 



fig. 6. 

 Pleurophorus subellipticus, Meek, 1867, Amer. Journ. Sei. and Arts., vol. xliv., new ser., p. 181. 

 Modiola 1 subelliptica, Meek, Fin. Rep. U.S. Geol. Sura. Nebraska, 1872, p. 211, pi. x. fig. 5. 



Specific Characters. — Shell small, transversely triangular, comparatively convex. 

 The anterior end is small, narrow and rounded. The posterior end comprises about 

 four-fifths of the valve. The anterior border is narrow and elliptical. The lower border 

 descends slowly, meeting the posterior with a broad, blunt curve. The posterior margin 

 is very oblique and somewhat convex in contour, making an obtuse angle above with 

 the hinge line. The latter straight, equalling in length almost half the antero-posterior 

 diameter. The umbones are small, placed far forward, but not terminal. Well marked, 

 rounded, oblique swelling, which gradually becomes obsolete, extends from the umbo to 

 the postero-inferior angle. Above the ridge the dorsal slope is rapidly compressed, and 

 below it there is a well-marked byssal compression. 



Interior. — Not exposed. 



Exterior. — The surface is adorned by close, fine, concentric lines of growth. 



Dimensions. — Specimen No. Tl712 B measures: antero-posteriorly, 7 mm.; dorso- 

 ventrally, 3 mm. 



