114 
THE AVONIAN OP THE AVON GORGE 
‘ back slope,’ is a massive bed which teems with uncrushed 
specimens. All the characters of the fossil can be readily made 
out in the numerous cross sections exposed in the rock face, 
but solid specimens are very difficult to extract. 
Productus ^ is a common fossil but is difficult to determine 
from the specimens seen in situ, which are usually mere cross 
sections or partially exposed valves. Specimens can however 
often be picked up from among the debris which is littered over 
the slopes. (The same level on the opposite side of the river is, 
however, a better hunting-ground.) 
Productus semireticulatus, mut. Si is represented by crushed 
valves and long spines in the shaley partings. The best collect- 
ing level is just above the ‘ front slope,’ where the weathered 
surfaces are covered with the spines of this Productus,^ 
associated with the tails of a small ‘ Phillifsia ’ and with abun- 
dant specimens of Heterotrypa cf. tumida. 
Athyris cf. flanosulcata is common at the same level on the 
opposite side of the river. 
Heterotrypa cf. tumida is abundant at several levels in the 
shaley partings and good specimens can be obtained from the 
Trilobite Bed. Fenestellids are common associates. 
Gasteropods belonging to several genera can be seen cross- 
sectioned in the rock faces, especially at the top of the sub- 
zone. 
S2 : Subzone of Productus corrugato-hemis'pTiericus 
(_ aff Cora, mut.). 
Fauna: — 
Throughout the South-Western Province very few gentes are 
represented in this subzone, but those which occur are remark- 
ably rich in individuals. Lithostrotion, Syringopora, Seminula, 
papilionaceous Chonetes, and variants of Productus hcmi- 
sphericus build up thick bands and recur again and again. 
1 This level lias often been referred to as the ‘ longispinus bed,’ but the 
designation is unfortunate since the Productus, whose spines have sug- 
gested the name, is very different from Productus longispinus. The term 
‘ Trilobite bed ’ is to be preferred. 
