Gallery 
VIII. 
Table-case 
14. 
Table-case 
15. 
138 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
beds of Beer, in Devonshire, and Westbury, near Bristol. 
ylviculd coutuvld is the best known, as giving a name to a 
widely distributed horizon of Bhaetic Age. like the Bhaetic 
shells generally, it is relatively small, perhaps in conse- 
quence of brackish water. Monotis decussala and Chlamys 
vcdoniensis are also important. There is a small but inter- 
esting series from the Keuper Marls of Warwickshire. The 
Conchyliau Age has no shell-bearing rock in this country. 
Permian. This Epoch is represented by marine shells 
from the Magnesian Limestone of Durham and the red marls 
near Manchester. Note Monotis speluncuria and Byssoarca 
striata from the former, and the tiny llissoa and Tarho from 
the latter. Bakcvxllia antiqna comes from both localities, 
and from Tyrone as well. 
Fig. 73. — Recent and fossil shells of Pleurotmiaria. a, P. Quoyana, now 
living in the West Indies ; b, P. plahjspira from the Middle Lias of 
France. The slit s receives the projecting anus, and, as the shell 
grows forward, is filled up by shell-substance. Both figures are less 
than natural size. 
Carboniferous. The shells of this Epoch come mainly 
from the C(jal Measures and the Mountain Limestone, the 
rocks of Middle Carboniferous or ]\Ioscovian age having 
yielded few mollusca in this country. The Coal Measures, 
though largely of fresh or brackish water origin, contain 
many marine bands ; the Lower Carboniferous rocks are all 
marine. The fossils have not here been separated according 
to age or rock or habitat. It will, however, be noticed that 
the Coal Measure fauna, and particularly the freshwater 
elements in it, occur among the lamellibranchs, whereas the 
gastropods are almost all from the Mountain Limestone. 
Among the Coal i\Ieasure fossils are many described by 
Sowerby in Prestwick’s classical memoir on Coalbrookdale, 
and many described by Dr. Wheelton Hind in the Mono- 
graphs of the Palaeontographical Society. The fresh-water 
forms include Anthracomya and Carbonicola \Antliracosia\ 
