MUTIELLA. 161 



species is rare, and the opinions expressed by various authors appear to have been 

 based entirely on the figures given by Sowerby. 



The hinge is similar to that of Mutiella coarctata (Zittel), 1 but shows some points 

 of difference : thus the transverse corrugations or teeth on the expanded anterior 

 margin appear to be absent, and the terminal posterior lateral tooth cannot be 

 recognised with certainty. The points of resemblance, however, and the similarity 

 in the form of the shell and the character of the ornamentation seem sufficient 

 to justify the assignment of this species either to Mutiella or to a closely 

 allied genus. 



From the figures given by Sowerby, Petricola nuciformis appears to differ con- 

 siderably from 1\ canaliculate/,, but after an examination of the type of the former 

 I am led to the conclusion that it is not specifically distinct from the latter ; it 

 differs only in being more inequilateral, and the apparent difference in the orna- 

 mentation is due to the imperfect preservation of the surface of the shell in 

 P. nuciformis. 



Types. — From Blackdown. The type of Petricola canaliculata cannot be found. 

 The type of P. nuciformis is in the Bristol Museum. 



Distribution. — Upper Greensand (zone of SclduenbaeJcia rostrata) of Blackdown, 

 and Peak Hill, near Sidmouth. 



Mutiella rotundata (d'Orbigny), 184-4. 



1844. Corbis rotundata, A. d'Orhi/jny. Pal. Frau<;. Terr. Cret., vol. iii, p. 113, 



pi. eclxxx, figs. 1-4. 

 1850. Prodr. de Pal., vol. ii, p. 102. 



1807. E. Gueranger. Album Paleont. de la Sarthe, p. 15, 



pi. xix, tigs. 10, 11. 



1870. F. Burner. Geol. v. Oberschles., p. 340. 



1871. Mutiella rotundata, F. StoliczJca. Palaeont, Iudica, Cret Fauna S. Iudia, 



vol. iii, pp. 247, 252. 

 1890. Corbis rotundata, A. J. Jukes-Browne and W. Hill. Quart. Journ. Geol. 



Soc, vol. Iii, p. 153. 



A portion of a right valve of Mutiella rotundata from the Cenomanian (Bed 11) 

 of Dunscombe, South Devon, was found and determined by the late C. J. A. 

 Meyer. An internal cast was collected from Bed 10 of Beer Head by Mr. Jukes- 

 Browne, who also records the species from the Chloritic Marl of Maiden Bradley, 



1 Fimbria coarctata, Zittel, 'Die Biv. d. Gosaugeb.,' pt, i (1864), p. 44, pi. vii, fig. 5. Eeferred by 

 Stoliczka, and subsequently by Zittel and by G. Midler, to the genus Mutiella. Compare also the 

 hinge of Mutiella rotundata figured by Gueranger, 'Album Paleont. de la Sarthe' (1807), pi. xix 

 fiir. 11. 



