252 LIAS OF ENGLAND AND WALES : 
It should also be mentioned that the form usually identified as Ammonites 
serpentinus is considered by Mr. S. S. Buckman to be A. falcifer ; he would, 
therefore speak of the zone as that of Ammonites falcifer. In the majority of 
cases, however, these so-called species have not been distinguished ; by many 
authorities they are regarded as synonymous, and in the following pages the 
name A. serpentinus will be used in a comprehensive sense, to include the 
varietal forms or "mutations" sometimes separately indicated as A. falcifer, 
and A. Strangwaysi. 
The zone of Ammonites communist ia usually taken to include 
the mass of clays between the Basement Beds and the sands and 
clays of the zone of A.jurensis ; in this sense it is here adopted, 
although Prof. Judd and others have employed it as a general 
term tor both Basement Beds and overlying clays.* Other 
divisions have been suggested, and to these references are made 
in the sequel. Locally the zone may, to some extent, be represented 
in the Basement Beds, as in Dorset and parts of Somerset. 
On the whole these clays yield many fossils, but locally some 
beds are comparatively unfossiliferous, the shells probably having 
been destroyed ; for selenite, in these instances usually abundant, 
may be regarded as the product of their decomposition and of that 
of iron-pyrites. 
Zone of Ammonites communis. 
Ammonites bifrons (Fig. 74). 
commnnis (Fig. 73). 
cornucopia (Fig. 71). 
crassus. 
elegans (Fig. 75). 
exaratus. 
fibulatus (Fig. 72). 
heterophyllufi (Fig. 76). 
Holandrei. 
Levisoni. 
lythensis. 
semicelatus. 
serpentinus (Fig. 70). 
- subcarinatus. 
Belemnites apicicurvatus. 
elongatus. 
ilminsterensis. 
subtenuis. 
Voltzi (Fig. 79). 
vulgaris. 
Nautilus astacoides. 
Cerithium armatum. 
Trochus duplicatus. 
Turritella Dunkeri. 
Dentalium liassicum. 
Astarte striato-sulcata. 
Avicula substriata. 
Cucullsea elegans. 
* Geol. Rutland, p. 89. 
