100 PERMIAN FOSSILS. 
(?) Propucta spinosa, J. Sow. J. de C. Sowerby, Sedgwick, Trans. Geol. Soc., 2d series, 
vol. ii, p. 119, 1829. 
(2) Propucta toneisPina, Sow. De la Beche, Geol. Man., p. 384, 1831; Germ. Transl., 
p. 459, 1832; 3d Eng. Ed., p. 573, 1833. 
StropHaLosiA Morristana, King. De Verneuil, Bull. de la Soc. Géol. de France, 
2™° serie, vol. i, p. 30, 1844. 
= — 5 Geol. Russ., vol. i, p. 222, 1845. 
— — as King, Annals and Mag. Nat. Hist., vol. xvi, 
p- 28, 1847. 
ae = a King, Catalogue, p. 9, 1848. 
Propvctus s SPINIFERUS, King. Howse, Trans. T. N. F. C., vol. i, p. 257, 1848. 
(?) ORTHOTHRIX LAMELLOSUS, Geinitz. Versteinerungen, p. 14, pl. v, fig. 16, &c., 1848. 
PRoDUCTUS CANCRINI, De Verneuil. Op. cit., p. 16, pl. vi, figs. 17-18 a, 6, 1848. 
Diagnosis—“ Form rounded. Both valves marked with numerous fine broken 
lines radiating from the nucleus. Area wide, and slightly elevated. Dorsal valve 
slightly convex,’ irregularly wrinkled longitudinally on the side, with several spines, 
rather long, adpressed and directed forward on the back, erect and directed backward 
on the umbone and sides. Ventral valve somewhat concave. Umbone small and much 
impressed.” (King.) 
Strophalosia Morrisiana is undoubtedly closely related to the Rasa species, 
Strophalosia (Productus) Cancrint of De Verneuil; but the following tabular comparison 
will show that both species possess certain well marked distinctive characters. 
S. Morrisiana. S. Cancrini? 
Slightly convex. Very convex. 
As wide as long; often wider. Longer than wide. 
Lateral slopes gradually inclining, and plicated Lateral slopes rapidly inclining, and plicated 
longitudinally. transversely. 
Area decidedly obvious. Area scarcely perceptible.* 
There appears to be some other differences, as in the striae and spines, and in the 
form of the small valve; but these I cannot insist on, in consequence of having no 
specimens by me of the Russian, to compare with the English species. 
Two varieties of Strophalosia Morrisiana occur in the Permian rocks of Durham. 
One has the large valve slightly convex, with a very small umbone; and appears to 
be confined to Tunstall Hill (this variety is represented in Plate XH, figs. 18, 19): in 
the other, which is rather common at Humbleton Quarry, the corresponding valve 
is more rounded, and the umbone more prominent (it 1s represented in the same 
1 Incorrectly printed in my ‘ Catalogue’ ‘“ roundly convex.” 
Catalogue, p. 9, 1848. 
3 Vide Geol. Russ., vol. ii, pp. 273-5, pl. xvi, fig. 8 a, 6, ¢; pl. xviii, fig. 7. 
4 The area, which I presume exists, appears to be so small that it has escaped the observation of 
M. de Verneuil. 
