LOWER CHALK — CHARACTERISTIC FOSSILS. 
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3. Fossils of the Lower Chalk. 
The fauna of the Lower Chalk, as a whole, comprises a very diffe¬ 
rent assemblage of species from that which is found in the Gault of 
Folkestone or in that part of the Upper Greensand which represents 
the Upper Gault; in other words, it differs much from the fauna 
which is essentially Selbornian, A certain number of species,however, 
which make their first appearance at the top of the zone of Pecten 
asper become more abundant in the Lower Chalk, and some species 
like Pecten orbicularis and Lima globosa range up from the Gault 
itself; so that there are many links between the one fauna and 
the other. 
The following is a brief resume of the fauna of the Lower Chalk, 
with lists of the commoner and most characteristic fossils of this 
stage: — 
Reptilia. — Ichthyosaurus campylodon and Polyptychodon inter- 
ruptus range up from the Gault, and are not uncommon in the 
Lower Chalk. A remarkable Dinosaur, Acanthopholis horridus, 
also occurs, and the tooth of an Iguanodon, found by Mr. W. Hill 
near Hitchin, proves that this genus also continued to live on the 
land areas which bordered the Cretaceous seas. 
Pisces.— Remains of Fishes are common in Lower Chalk, but 
generally in the form of teeth. The crushing palatal teeth of Ptycho- 
dus. often occur, the commonest species being Pt. decurrens. They 
are sometimes called “ fossil slugs ” by quarry men. Teeth of various 
Sharks, such as Lamna appendiculata , Oxyrhina Mantelli, Corax 
falcatus, and Notidanus microdon frequently occur, but all these 
species range up into the Upper Chalk. Of Teleostean Fishes, 
Beryx ( Ctenothrissa ) microcephalus and Hoplopteryx lewesiensis 
may be mentioned. 
Cephalopoda.— These became very abundant, and a large number 
of species belonging to many genera have been found in the Lower 
Chalk ; they are, however, much more abundant in the lower 
than in the higher beds of the stage. The following list comprises 
the commoner and more important species, and shows their range, 
so far as it is at present known, the letter c indicating that the 
species is common, r that it is rare, and a + that it is moderately 
common. 
