FOSSIL MARINE UNIVALVES. 427 
_ tubercles ; but the casts present only the smooth surface of 
the interior of the shell in which they were moulded. 
In the most ancient fossiliferous formations, the Carboni- 
ferous, Devonian, and Silurian, many species and genera of 
Lien. 135. UNIVALVES, FROM THE CHALK OF TOURAINE.—nat. 
Fig. 1.—Conus TUBERCULATUS, with part of the shell remaining 
attached to the cast. 
2.—SoLARIUM ORNATUM, with the shell. 
2a.—Specimen of the same species, deprived of the shell. 
Gasteropoda have been discovered. Professor Phillips enu- 
merates more than ninety in the mountain limestone of 
Yorkshire (Phil. York.), belonging to the genera Z'urbo, 
Pleurotomaria, Natica, Euomphalus, Loxonema, Macrocher- 
lus, Platyceras, and Metoptoma. Thirty-four species from 
the Silurian rocks are figured and described in Murch, Sil. 
Syst. p. 706. 
The Natica, Lign. 136, fig. 3, sometimes attains thrice 
the size represented, and has been found in many localities 
in England and Ireland. 
PrevroTomaRia. Lign, 136, fig. 4.—This is an extinct 
genus, distinguished from Z’rochus by a fissure on the right 
lip, the position of which is indicated by the band along the 
