266 Prof. W. King's Notes on Permian Fossils. 



Strophalosia Morrisiana. Strophalosia Cancrini. 



Large valve. 



Slightly convex, and evenly Strongly convex, and swelled 



rounded. out on the posterior half. 



Transversely elliptical (wider " A little longer than wide." 

 than long). 



Lateral slopes gradually in- Lateral slopes nearly per- 



clined, and marked with longi- pendicular and transversely 



tiidinal furrow-wrinkles. wrinkled. 



Area well defined. Area so imperceptible as not 



to be noticed by l)e Verneuil, 

 Keyserling, or De Koninck. 



Umbone very slightly affect- Umbone decidedly pi'omi- 



ing the even roundness of the nent, pointed, and incurved 



valve, decidedly impressed or over the cardinal edge, 

 truncated, and scarcely curving 

 down to the cardinal edge. 



Hinge-line a little more than Ilinge-line not much shorter 



half the width of the valve. than the width of the valve. 



Obsoletely striated. Decidedly striated. 



There appear to be some other differences, as in the spines, 

 the nucleus of the small valve, &c. ; but those tabulated are quite 

 sufficient to demonstrate that both forms are specifically distinct. 

 The specimen of Strophalosia productoidea figured by De Ver- 

 neuil* has more resemblance to S. Morrisiana than to S. Can- 

 crini : the Devonian species, however, is too convex ; and its area 

 is too wide, and not quite high enough for the Permian form. 



As regards the variety Humbletonensis, I am more than ever 

 inclined to consider it as a distinct species, the possibility of 

 which I was, on a former occasion, impressed withf. At that 

 time I also alluded to its being more closely related to S. Can- 

 crini than the typical forms of S. Morrisiana ; as it appeared to 

 graduate the one into the other. But I am not yet either dis- 

 posed to admit its identity with the former, or prepared to say 

 positively that it is specifically distinct from the latter. The 

 following description may assist in drawing \x^ a diagnosis, 

 should it hereafter be considered as a species. 



General form rather strongly convex ; as wide as long, some- 

 times longer than wide, rarely the converse. Large valve rather 

 strongly convex and evenly rounded ; occasionally with one or 

 more longitudinal wrinkles on the sides ; furnished with nume- 

 rous long somewhat irregularly arranged spines, creeping and 



* Russia ill Europe, vol. ii. pi. IS. fig. 4 e,f. 



t Vide Monograph of the Permian Fossils of England, p. 101. 



