UPPER, OR FLINTY CHALK. 207 



that occur in Sussex by specific names; since the specimens present no 

 remarkable character, and although of various shapes, and degrees of 

 convexity, are probably only varieties of one species. 



The shells figured by Mr. Smith, are of frequent occurrence in the 

 Upper chalk, near Lewes, and are commonly attached to other bodies; 

 they appear to be the upper and under valves, of the same species. They 

 are nearly flat, of a suborbicular form, their margins very thin, and much 

 expanded. 



74. Ostrea . Tab. xxv. fig. 4. 



This shell is rather depressed, of an oblique, ovate form, the external 

 surface scabrous, the margin thin, and undulated by five or six depressions. 

 The hinge is tripartite, marked with transverse phcae, and the adjoining 

 edge of the shell on each side, has a row of crenulated indentations ; the 

 inner border of the hinge is straight, and rendered very distinct by a 

 deep hollow that extends beneath it. The inner surface is marked with 

 a few gentle concentric ridges. The muscular impression is shght. 



Three or four examples have been discovered with the characters 

 above enumerated very distinctly marked, while others occur in which 

 they are but obscurely expressed ; it is not improbable, that in a suite of 

 specimens, the present variety may pass insensibly into the flat oyster, 

 previously noticed. 



Locality. Upper chalk, near Lewes. 



75. Teredo . Tab. xviii. fig. 23. 



The Teredo navalis, or ship-worm, is well known for its depredations 

 on the hulls of vessels, which in warm climates, it sometimes completely 

 destroys. The fossil, like the recent species, is found inhabiting cavities 

 which it has formed in blocks of wood ; and the wood, with the shells 

 imbedded, is frequently discovered in a petrified state, in many parts of 

 England*. 



* Specimens of this kind are figured by Parkinson, Org. Rem. Vol. i. PI. viii. fig. 9- 

 They are very abundant in the London clay; some of the finest examples known were collected 

 by the author on the banks of the Regent's Canal. 



