PLATE 9:3. 



Fig. \ a- d. Chonetes complanata. 418 



1 a. An impression of the outside of the ventral valve of this species. 



1 6. A similar impression in sandstone, showing the concentric lines of growth. 



1 c. A cast of the interior of a ventral valve, showing the muscular impression and cavities of 



the dental lamellae. 



2 c ( in centre of plate, by error for Id). An enlargement of the imprint of the surface, as 



sometimes seen in sandstone. 



Fig. 2 a, & 3 a, i. Stropiiodonta linckl^ni. 415 



2 a (the specimen referred with doubt to this species). Tlic exterior of a ventral valve, in 



wliich the shell is partially exfoliated. 



3 o. The imprint made by the interior of the dorsal valve of a small individual, showing the 



cavities made by tlie bifurcating cardinal process, the impressions of the median crest, 

 and the low ridges towards the centre of the shell. 



3 b. The impression of a larger ventral valve of this species, showing the same features as the 

 preceding, the crenulated hinge-line, and the abruptly recurved outer margin. 



F\g.2h,c? Strophodonta vascularia. 412 



2 b, c are referred to tliis species with some hesitation : they are the impressions of the ex- 

 terior of the dorsal valve, and show the convexity corresponding to the concavity of the 

 shell, which only occurs in an equal degree in this or the preceding species; the others in 

 the rock being much less concave on the dorsal side. 



Fig. 4. Strophodonta magnifica. 414 



4. The cast of a ventral valve, preserving the marks of the muscular impression and tlie 

 imprints of the radiating striae. 



