GASTEROPOD FAUNA IN THE MILLSTONE GRIT OF SCOTLAND. 345 



Protoschizodus curtus, Meek and Worthen, sp., 1866. (PI. I. figs. 22, 23.) 



Schizodus curtus, Meek, 1866, Proc. Chicago Acad. Sci., vol. i. p. 18. 



,, rossicus, Geinitz, 1866, C'arb. und Dyas in Nebraska, p. 18, Tab. i. fig. 28. 

 ,, curtus, Meek and Worthen, 1872, Fin. Rep. U.S. Geol. Sure. Nebraska, p. 208, pi. x. 

 fig. 13, a, b, c, dl, e. 



Specific Characters. — Shell triangularly suborbicular, moderately gibbose, almost 

 equilateral. The anterior margin almost straight above, oblique, bluntly rounded below 

 in the inferior border, which is broadly convex. The posterior margin is narrowed, 

 straight, obliquely truncate. Hinge line arched short. The umbones are well marked, 

 raised, pointed, moderately gibbose, and central. Passing from the umbo obliquely to 

 the postero-inferior angle is a well-marked angular ridge which separates the convex 

 portion of the valve from the rapidly compressed dorsal slope. 



Interior. — Muscle scars normal. 



Exterior. — The surface is almost smooth, but obscure concentric lines of growth are 

 apparent near the lower margin of the valve. 



Dimensions. — PI. I. fig. 22. Specimen No. Tl982 B , a right valve, measures: 

 antero-posteriorly, 16 mm. ; dorso-ventrally, 15 mm. 



Localities.— Stirlingshire, Torwood Glen, 2^ miles N.W. of Larbert, 9 to 10 feet 

 above Castlecary Limestone ; Linlithgow, river Avon, right bank, between Railway 

 Viaduct and outcrop of Castlecary Limestone ; Greenfoot Moulding Sand Quarry, near 

 Gain Farm, Dumbartonshire. 



Observations. — Protoschizodus curtus resembles very closely P. sub&qualis, de 

 Kon, from the upper beds of Carboniferous Limestone of Thorpe Cloud, Upper Dibuno- 

 phyllum zone ; but the Scotch examples are less gibbose, more triangular, and have a 

 more oblique, straighter anterior border. The umbones are more subcentral and more 

 elevated. Meek and Worthen recognised the close resemblance between the American 

 shell and Schizodus rotundatus of the Permian. I think they were right in separating 

 the species for several reasons. In the first place, S. rotundatus was established on a 

 single example, and I believe has not been figured since King's monograph was published 

 in 1841 ; and we learn from the note on the explanation of the plate that "the figure 

 makes the specimen more perfect than it really is." It is important, however, to note 

 the close relationship between the three forms. 



I have referred the species to Protoschizodus on account of its general shape and 

 contour. This species is fairly common in at least two of the Scotch localities. 



Schizodus Wheeleri, Swallow, sp., 1862. (PI. I. figs. 22-28.) 



Cypricardia ? Wheeleri, Swallow, 1862, Trans. St Louis Acad., vol. i. p. 96. 



Schizodus obscurus, Geinitz, 1866, Carb. und Dyas in Nebraska, p. 20, Tab. i. figs. 30, 31. 



„ Wheeleri, Meek and Hayrlen, Fin. Rep. U.S. Geol. Surv. Nebraska, p. 209, pi. x. fig. a, 

 b,c,d, (e,f1). 



Specific Characters. — Shell moderately gibbose ; dorsal slope much compressed, 



