PINNA. MYTILUS. MODIOLA. 407 
be readily distinguished, There are about fifteen or sixteen 
British fossil species. The earliest appearance of this genus 
is in the Carboniferous Limestone of Derbyshire (Phil. York. 
tab. 6), in which there are two species. The Lias contains 
one species; the Oolite eight ; the Cretaceous formation 
four ; and the London clay two. One of the tertiary species, 
Pinna afinis (Min. Conch. tab. 313), occurs in considerable 
numbers in the Bognor rocks, associated with Pectunculi ; 
it varies in length from one to six or seven inches. A beau- 
tiful and delicate species is found in the Calcaire grossier of 
Grignon. Shells of this genus are very rare in the White 
Chalk, most of the supposed Pimne being imperfect exam- 
ples of Inoceramt ; but I have seen specimens from Norfolk 
(collected by the late Mr. Woodward), and one from Sussex, 
in the cabinet of the Marquess of Northampton.* 
Mytiztus, orn Mussen.—There have been found about 
twenty species of this well-known genus of marine shells in 
the British strata. They are sparingly distributed through 
the several formations, from the Silurian to the newer 
Tertiary. One species (Mytilus Lyelli, Wond. p. 405, fig. 
2) occurs in the Wealden, associated with fresh-water shells. 
Of the genus termed Moprona, which comprises those 
mussels that have a rounded anterior termination, nearly 
forty British species have been discovered ; ranging through 
the fossiliferous strata, from the Silurian to the Crag. A 
beautiful species (Modiola elegans. Min. Conch. tab. 9), with 
the shell generally retaining its pearly coat, is found in the 
London Clay, and in the limestone of Bognor. 
An undescribed striated MJodiola (which may be named 
* Dr. Lee has recently discovered in the Kimmeridge Clay on his 
estate at Hartwell, Bucks, a species of Pinna not previously observed 
in England. Professor Forbes informs me that it resembles Pinna 
conica (of Roemer), and is related to P. lanceolata of Sowerby, but 
appears to be distinct from both. 
