344 DR WHEELTON HIND ON THE LAMELLIBRANCH AND 



Locality. — Torwood Glen, Stirlingshire, 8 to 10 feet above the Castlecary 

 Limestone. 



Observations. — A single specimen of this shell has occurred, a left valve, and I have 

 referred it to Meek's species. The American shell reaches about 25 mm. in its trans- 

 verse diameter, and therefore we must regard the Scotch specimen as immature. 



Grammatodon tenuistriata, Meek and Worthen, sp., 1872. (PI. I. fig. 21.) 



Macrodon tenuistriata, Meek and Worthen, 1867, Proc. Chicago Acad. Set., i. p. 17. 



Area striata, Geinitz, 1866, Garb, und Dyas in Nebraska, p. 20, pi. i. fig. 32. 



Macrodon tenuistriata, Meek and Hayden, 1872, Fin. Rep. U.S. Geol. Surv. Nebraska, p. 207, 



pi. x. fig. 20, a, b. 

 Parallelodon tenuistriata, Bolton. 1907, Q. J. Geol. Soc, p. 460, pi. xxx. fig. 12. 



Specific Characters. — Shell small ; somewhat transverely oblong, gibbose. The 

 anterior end is bluntly rounded, the antero-superior angle well marked. The inferior 

 and superior borders sub-parallel. The hinge line straight, the lower margin very 

 slightly convex, deeply indented above its centre for the byssus. The posterior end 

 obliquely truncate, almost straight. The umbones are turned, raised, incurved, and 

 pointed, placed at the junction of the anterior and middle thirds of the hinge line. The 

 body of the valve is convex, deeply indented towards the margin of the byssal sulcus. 

 The dorsal slope is as much compressed as to be concave. It is separated from the rest 

 of the valve by a well-marked angular ridge, which extends from the umbo to the 

 postero-inferior angle. 



Interior. — Normal. 



Exterior. — The general surface of the valve is ornamented by the decussation of the 

 concentric lines of growth by close radiating lines. The latter become so much stronger 

 on the dorsal slope as to form strong radiating ridges. 



Dimensions. — PI. I. fig. 21. Specimen No. Tl812 B measures : antero-posteriorly, 

 12 mm. ; dorso-ventrally, 7 mm. 



Locality. — Linlithgow, right bank of river Avon between the Railway Viaduct and 

 the outcrop of the Castlecary Limestone, and in the Bilston Burn section, Midlothian. 



Observations. — G. tenuistriata, M. and H., is closely allied to G. semicostatus, 

 M'Coy, of which it is probably a mutation. It is, however, much less transverse, deeper 

 and more gibbose. 



Only two examples of the species are in the collection. G. semicostatus is very 

 abundant at a horizon a very little below that in which G. tenuistriata occurs, namely, 

 below the Linn Spout Limestone. Mr H. Woods has shown {Ann. Mag. Nat. Hist., 

 1899, ser. 7, vol. iii. p. 47) that the name Grammatodon, Meek and Hayden, is prior 

 to Parallelodon of the same authors, and must replace it. It appears that Macrodon of 

 Lycett, founded for a Jurassic shell, was occupied for a genus of fishes and cannot 

 therefore be used, and that there is no essential difference in the type of the hinge of 

 the Carboniferous and .Jurassic forms. 



