BRITISH AVONIAN CONODONT FAUNAS 39 
first appearance of Spathognathodus cf. robustus (Branson & Mehl), S. tvidentatus 
(E. R. Branson) and S. anteposicornis Scott. 
REMARKS : This zone occupies nearly all the Upper K Zone in the North Crop 
and the lower part of the Upper K Zone in the Avon Gorge (Samples K 12—KgI in the 
Avon Gorge and Samples KL 16-KL 18 on the North Crop). It is correlated with 
the Upper Cu I and basal Cu II « of West Germany, the lower part of the Upper 
Hannibal Formation of North America and with part of the Tne, of Belgium. 
On the North Crop a covered shale interval is present between Samples KL 13 
and KL 16. Inthe Avon Gorge Samples K 12-K 17 contain P. variabilis gen. et sp. 
nov. and S. plumulus s.s. sp. nov., associated with the P. inornatus group. On the 
North Crop (Samples KL 16-KL 18) P. variabilis gen. et sp. nov. and S. plumulus s.s. 
sp. nov. are absent from the zone. __S. tsosticha (Cooper) has not been found in the 
Avon Gorge, but there is a concealed interval above K 17 and below Kg1. There 
are thus two subzones within this assemblage zone. The lower corresponds to 
Samples K 12-K 17 in the Avon Gorge and occupies the covered interval between 
KL 13 and KL 16 on the North Crop ; the upper subzone (KL 16-KL 18 of the 
North Crop) occupies the concealed interval above K 17 and below Kel in the 
Avon Gorge. 
Spathognathodus cf. robustus—Spathognathodus tridentatus 
Assemblage Zone 
CHARACTERISTIC SPECIES :_ S.cf. vobustus (Branson & Mehl), S. elongatus (Branson 
& Mehl), S. tvidentatus (E. R. Branson), S. crassidentatus (Branson & Mehl) and S. 
anteposicornis Scott. 
Limits : The base of this zone is marked by the first occurrence of Spathognathodus 
cf. vobustus (Branson & Mehl), S. tvidentatus (E. R. Branson) and S. anteposicornis 
Scott. 
The top of the zone is marked by the first occurrence of Spathognathodus costatus 
costatus (E. R. Branson). The final appearance of the Polygnathus inornatus group 
is within the lower part of the zone. 
REMARKS : This zone occupies the upper part of the Upper K Zone in the Avon 
Gorge (Sample Ker) and the uppermost K and basal Z Zone on the North Crop 
(Samples KL 19-ZLA 1). It is correlated with the upper part of the Hannibal 
Formation of North America, with the Lower Cu II « of Germany and with the 
Upper Tng, of Belgium (see also p. 56). 
The lower part of this zone (with the P. inornatus group) probably occurs in the 
concealed interval beneath Sample Ket in the Avon Gorge. 
Spathognathodus costatus costatus—Gnathodus delicatus Assemblage Zone 
CHARACTERISTIC SPECIES: In both the Avon Gorge and the North Crop: S. 
costatus costatus (E. R. Branson), S. costatus sulciferus (Branson & Mehl), S. cf. 
cristulus Youngquist & Miller, S. cyrius (Cooper), S. crassidentatus (Branson & Mehl), 
G. delicatus Branson & Mehl, Ligonodina beata nom. nov., Hindeodella corpulenta 
