NIAGARA GEOUr. 



265 



Fig. 5 m. A large specimen, having the form well preserved, but the angles at the extremities of 



the hinge-line worn off and rounded. 

 Fig. 5 n. Front view of the specimen fig. 5 h. 



Fig. 5 o. Cardinal view of a small specimen, where the area is nearly closed. 

 Fig. 5 p. Cardinal view of a specimen where the lower part of the shell is compressed, leaving 



the area exposed to a greater extent than in ordinary specimens. This specimen 



shows also that the ventral valve has a narrow area and a partial foramen. 

 Fig. 5 r. The interior of a dorsal valve, showing the strong lamella on each side of the triangular 



foramen, extending down to the centre of the valve, with a central stronger one. 

 Fig. 6 s. An enlargement of the strias. 

 Fig. 5 t. Section of the plications, showing their form and the number of striae upon the surface. 



Position and locality. In the shale of the Niagara group at Wolcott, Rochester, Sweden, 

 Lockport, and near Lewiston on the Niagara river. 



452. 3. SPIRIFER RADIATUS. 



PL, LIV. Fig. 6 a -/. 



For references and synonymes, see page 66 of this volume. 

 Ddthyris cyrtana. Dalman, Vet. Acad. Handl. 1827, t. iii, f 4. 

 Delthyris bialveatus. Conrad, Jour. Acad. Nat. Sciences, Vol. viii, p. 261. 



I am unable to distinguish any difference between the S. radiatus and the specimen figured 

 by Mr. Conrad, which is broken and otherwise mutilated. This shell does not always present 

 the same appearance in the soft shale of the Niagara group as in the limestone of the Clinton 

 group, but there is no evidence of the existence of a distinct species. The width of the area is 

 variable, and so also the form of the foramen, which is often triangular, and sometimes long 

 and nearly linear, varying with the proportions of the area. The striae are flat, bifurcating, and 

 rarely interrupted by lines of growth. 



M. DE Verneuil cites* the S. cyrtcRiia of Dalman as occurring at Lockport with .S'. niaga- 

 rensis, and occupying the same position as in Europe. A careful comparison of our specimens 

 with specimens of S. cyrtcena from Gothland, and specimens of S. radiatus of Sowerby from 

 Dudley, has convinced me that there is but a single species ; and our specimens show, in a 

 still greater degree, the variable character mentioned by Dalman. In the Swedish specimens 

 the margin is usually plicated, the rounded plications sometimes extending halfway to the beak ; 

 while in others they are only visible in the undulating outline, and sometimes are quite free 

 from such characters. This plication of the margin appears not to be unfrequent in the Dudley 

 specimens, judging from those I have seen, and we may therefore regard the specimens from 

 these localities as identical. In all the American specimens I have seen, there is no evidence 

 of this plication of the margin or surface, though in other respects they are almost identical 

 with the specimens from Dudley, and it is not easy to point out any important characters by 



*Note SUV le parallelisme dcs depots palseozoiques de I'Ameriiiue Septentrionale avec ceux dc I'Eiirope, &c. 



[Palaeontology — Vol. ii.] 34 



