152 
THE AVONIAN OF THE AVON GORGE 
Valves thick-shelled, large. 
Pedicle valve convex (often strongly so). 
Beak usually well-differentiated. 
Teeth, area, spines and tubuli as in Ghonetes. 
Muscular scars deeply impressed and arranged as in the 
giganteid Producti. An additional pair of circular 
adductor scars are placed below the principal adductors 
(as is often the case in the giganteid Producti). 
Brachial valve: 
Adductor scars deeply impressed and brachial ridges con- 
spicuous ; mesial septum and cardinal process strongly 
developed. 
Ornament: 
Fine, close-set longitudinal ribs. 
Spines practically absent, except from the cardinal edge. 
Bows of pits as in Ghonetes. 
Figures: compare Dav. Plates 45 and 55. 
Notes : — The genus Daviesidla was created by Waagen to include 
massive Productoid forms, with strongly- developed teeth and accessory 
adductors in the pedicle valve. The geno-type is Productus llangollensis, 
Dav. (Dav. Plate 55, figs. 9 and 10) and Ghonetes comoides (J. Sow.) is a 
syngeno-type (compare Dav. PI. 45, fig. 7). 
‘ Ghonetes ’ aff . comoides, figured above, agrees with ' Ghonetes ’ 
comoides in all essential points, although it never attains either 
the large dimensions or the thickness of shell which are so 
marked in that species. There can however be no hesitation 
in referring ‘ Ghonetes ’ aff. comoides to Waagen’s genus. . 
This species is very abundant in Di, in the South-Western 
Province. 
A difficulty arises however with regard to the classifica- 
tion of Ghonetes cf. 'papilionacea from S, and of Ghonetes cf . 
comoides from C. 
Ghonetes cf. papilionacea has a strongly Chonetoid aspect, since 
its beak region is not appreciably differentiated from the 
flanks and the apex of the beak is not incurved ; also, the 
valves are usually flattened. Hence, this form bears a strong 
