THE LOV/'EK LIAS OP KEYNSHAM. 
‘21 
division (whose index is Am. geometricus). This fossil satis- 
factorily links the series with the Ziphus zone of Glerman 
authors and, should it be considered better to include the 
lower division (indexed by Am. ohliqueco status) in the 
Arietes beds, there can be no doubt that Am. planicosta 
is the best index to choose for the upper subdivision. 
The Semicostatus beds of Keynsham if extended, as we 
suggest, so as to include a lower subdivision rich in the 
semicostate mutation. Am. ohliqueco status., form an excellent 
connecting link between the same beds at Radstock and 
Sodbury. 
At Radstock this zone includes the richly fossiliferous 
Spirifer Bank (the Spirifer Bank of German authors 
occurs on a higher horizon, namely, at the base of the 
Jamesoni zone, i.e., at the bottom of the Middle Lias). 
Here Am. sauzeanus and Am. semicostatus (both varieties) 
are the predominant forms amongst ammonites, whilst 
Spiriferina ivalcotti, Rh. lineata and a Terebratula identi- 
fied as Wald, indentata are the commonest forms amongst 
Brachiopods. The thickness of the zone is only a few 
inches. 
At Keynsham Am. planicosta takes the place of Am. 
sauzeanus, and Am. turneri occurs as an additional form. 
Amongst Brachiopods only R1i. semicostati is common, and 
this fossil is very nearly allied to the Radstock form of Rh. 
lineata. The thickness rises to nearly five feet. 
At Sodbury Am. Semico status and Am. turneri occur in 
vast numbers, whilst Brachiopods are excessively rare. In 
one point the Sodbury development is in closer relation 
to that of Radstock than to that of Keynsham, namely, in 
the fact that Gryphea arcuata is an associate of the semi- 
costate ammonites, whereas, at Keynsham, this fossil is 
absent from this horizon. The thickness is more than 
twenty-five feet. 
