258 



perhaps met with in any of the succeeding strata ; a shell 

 of the genus helicina, and the first simple unilocular shell 

 bearing a turriculated form, being a species of the genus 

 melania. 



In the strata above the lias, belonging to the under 

 oolite, as well as in those of the middle and upper oolite, 

 including the cornbrash, Kelloway rock, &c. numerous 

 genera are found which are not known in the preceding 

 subjacent formations. The small proportion which the 

 univalves bear to the bivalves, which was observable in the 

 preceding formation, is here more obvious. Various species 

 are found ofpecten, lima, astarte, trigonia, lutraria, mytilus, 

 modiola, venus, and isocardia, with the tubular shell vermi- 

 cularia, and the .single univalve solarium. 



In the superjacent green sand formation, including the 

 whetstone of Devonshire, many new genera of bivalves are 

 found : cardium, corbula, perna, dianchora, nucula, veneri- 

 cardia, occur here, with the simple turriculated shells of the 

 genus turritella, and the subglobose univalve auricula. Here, 

 also, are first found the multilocular turriculated shells of 

 the genus turrilites and the hooked shells of the genus 

 hamites. 



The blue marl and the chalk marl which next super- 

 vene, display the genera scaphites and inoceramus, with the 

 oval multilocular shells, distinguished in this work as ammo- 

 nellipsites and 7iautellipsites, and some other curiously 

 formed multilocular shells much resembling, in their general 

 characters, nautili and ammonitce ; and deriving their 

 peculiar forms, perhaps, merely from compression. 



The chalk, although containing many interesting species 

 of the genera which had appeared in preceding strata, has 

 perhaps only two genera of shells which originated in the 

 waters by which it was deposited, crania and magas. 



The fossil shells which are found in the immense stratum 

 of blue clay resting on the chalk, manifest that a consider- 



