PLASTIC CLAY F0RMATI0:N. 263 



Cuvier, " and also a fruit of a species of palm, with the vegetable fibres 

 quite distinct*." 



4. The casts of shells in the specimens figured, belong to the genera 

 cerithium, unio, and cyclas ; the species of the latter resembles the 

 Linnean Mactra solida, or subtruncata, which is also found abundantly 

 with cerithia, in the blue clay at Woolwich j-. 



5. Cexiihmm funatiim. Tab. xvii. fig. 4. 



A conical elongated shell, with two obtuse, crenulated, transverse 

 ridges on each volution. 



It consists of ten or eleven whorls, and is seldom found perfect. It 

 occurs in immense quantities in the blue clay (No. 8), and is sparingly 

 distributed in the oyster-bed (No. 10), and in the red marl (No. 7). 



6. Cerithium melanoides. Tab. xvii. fig. 3. 



Turreted, whorls convex, longitudinally undulated, transversely 

 carinated ; carinee tuberculated. 



This elegant species is found in the same stratum with the above, 

 but is easily distinguished by the sharp, tubercular, carinated ridges with 

 which it is ornamented, and the longitudinal depressions between the 

 tubercles. It is comparatively rare. 



7. HeHx ? Tab. xviii. figs. 19, 20. 



The delicate little shell, figured in the plate referred to, was found by 

 Col. Eirch, of Bath, in the blue clay (No. 8), of Castle-Hill. The mouth 

 is filled with clay, and the specimen is too fragile to permit its removal ; 

 the surface is perfectly smooth ; the spire elevated ; the volutions are 

 three in number. It has much the appearance of a fresh-water shell. 



8. Cytherea Scutellaria ? (of Webster). Tab. xxv. fig. 2. 



This fossil is from the blue clay (No. 9), which is almost entirely 

 composed of broken bivalves, apparently of the genera cytherea and 

 cyclas. A perfect example is exceedingly rare, and I have not yet been 

 so fortunate as to discover one ; the shell represented being the most 

 entire of any in my possession. 



* Geolog. Trans. Vol. ii. p. 191. t British Mineralogy, Vol. iv. p. 185. 



