38 BRITISH AVONIAN CONODONT FAUNAS 
In addition, on the North Crop two subzones can be delineated, the lower being 
characterized by the presence of Spathognathodus plumulus nodosus sp. et subsp. nov., 
Clydagnathus gilwernensis gen. et sp. nov. and Pseudopolygnathus vogesi sp. nov. 
The upper is recognized by the absence of the above-mentioned species and by the 
presence of Clydagnathus sp. nov. A. 
Siphonodella—Polygnathus inornatus Assemblage Zone 
CHARACTERISTIC SPECIES : Polygnathus inornatus inornatus Branson & Mehl, 
Polygnathus lobatus lobatus Branson & Mehl, Polygnathus lobatus inflexus subsp. nov., 
Polygnathus inornatus rostratus subsp. nov. and Siphonodella isosticha (Cooper). 
Limits: The base of this zone is marked by the first occurrence of Siphonodella 
tsosticha (Cooper), P. inornatus inornatus Branson & Mehl, P. lobatus lobatus Branson 
& Mehl, and P. inornatus rostratus subsp. nov. The top of the zone is marked by the 
Continuation of Fig. 13 caption] 
Cavusgnathus chavactus—inner lateral view. 54a. Cavusgnathus cristatus—inner lateral 
view. 54b. Cavusgnathus cristatus—oral view. 
Taphrognathus varians—Cavusgnathus—A patognathus Assemblage Zone. 55a. 
Taphrognathus varians—oral view. 55b. Taphrognathus varians—lateral view. 56a. 
Spathognathodus cristulus—oral view. 56b. Spathognathodus cristulus—lateral view. 
Apatognathus ? geminus—Cavusgnathus Assemblage Zone. 572. Cavusgnathus 
cristatus—inner lateral view. 57b. Cavusgnathus cristatus—oral view. 58. Apato- 
gnathus ? geminus—inner lateral view. 
Mestognathus beckmanni—Gnathodus bilineatus Assemblage Zone. 59a. Mestognathus 
beckmanni—inner lateral view. 59b. Mestognathus beckmanni—oral view. 60. Cavus- 
gnathus unicornis—inner lateral view. 61. Spathognathus scitulus—lateral view. 
62a. Apatognathus bladus sp. nov.—inner lateral view. 62b. Apatognathus bladus sp. 
nov.—outer lateral view. 63. Hibbardella abnoymis—inner lateral view. 64. Neo- 
prioniodus singulavis—lateral view. 65a. Gnathodus girtyi givtyi—oral view. 65b. 
Gnathodus girtyi givtyi—lateral view. 66a. Gnathodus bilineatus—oral view. 66b. 
Gnathodus bilineatus—lateral view. 
Gnathodus mononodosus Assemblage Zone. 67a. Gnathodus girtyi simplex—tiateral 
view. 67b. Gnathodus girtyt simplex—oral view. 68a. Gnathodus mononodosus sp. 
nov.—lateral view. 68b. Gnathodus mononodosus sp. nov.—oral view. 68c. Gnathodus 
mononodosus sp. nov.—aboral view. 69a. Gnathodus commutatus—lateral view. 69b. 
Gnathodus commutatus—oral view. 70a. Gnathodus homopunctatus—lateral view. ob. 
Gnathodus homopunctatus—oral view. 71a. Spathognathodus cf. cristulus—lateral view. 
71b. Spathognathodus cf. cristulus—oral view. 
Gnathodus girtyi collinsoni Assemblage Zone. 72a. Gnathodus girtyi collinsoni subsp. 
nov.—oral view. 72b. Gnathodus girtyi collinsoni subsp. nov.—lateral view. 73a. 
Gnathodus girtyt simplex—oral view. 73b. Gnathodus girtyi simplex—iateral view. 
74a. Gnathodus girtyi givtyi—oral view. 74b. Gnathodus girtyi girvtyi—lateral view. 
75a. Gnathodus nodosus—lateral view. 75b. Gnathodus nodosus—lateral view. 75c. 
Gnathodus nodosus—aboral view. 76a. Gnathodus mononodosus sp. nov.—lateral view. 
76b. Gnathodus mononodosus sp. nov.—oral view. 76c. Gnathodus mononodosus sp. nov.— 
aboral view. 77a. Gnathodus bilineatus—oral view. 77b. Gnathodus bilineatus—iateral 
view. 78. Prioniodina stipans—iateralview. 79. Prioniodina subaequalis—iateral view. 
80. Neoprioniodus scitulus—lateral view. 81. Neoprioniodus tulensis—lateral view. 
82. Ligonodina levis—inner lateral view. 
