208 UPPER, OR FLINTY CHALK. 



Portions of the tubular part of the shell, are the only vestiges that 

 occur in the Sussex chalk ; these are sometimes enclosed in fragments of 

 carbonized wood, but owing to the friable nature of the latter, are more 

 commonly found detached. The specimens are of a depressed, cyhndrical 

 form, more or less bent, and gradually tapering to a point. Their 

 diameter at the larger extremity, seldom exceeds half an inch ; their length 

 varying from one to six inches. The surface is smooth, and has numerous, 

 indistinct, annular elevations, and depressions, Uke the recent teredo ; of 

 which, in fact, the present species appears to be only a variety. 



Tab. xviii. fig. 23, represents the usual appearance of these fossils. 



Localities. Upper chalk, near Lewes, and Brighton. 



76. TeYehratuia. subrotunda. Min. Conch. Tab. xv. figs. 1, 2. 

 Circular, depressed, smooth; valves regular, equally convex; beak 



short. 



The width of this shell rather exceeds its length, which is seldom more 

 than 0-7 inch. The sides, near the beak, are somewhat angular. The 

 surface of the valves is smooth, and marked by fine, transverse lines of 

 growth. 



The lower, or beaked valve, has two hinge teeth, and the upper valve, 

 two corresponding grooves for their reception, from which two elongated 

 appendages proceed. This structure is beautifully represented by Mr. 

 Sowerby, in fig. 6. Tab. xv. 



Localities. Common in every part of the South Downs. 



77. Terebratula ovata. Min. Conch. Tab. xv. fig. 3. 

 Obovate, depressed, smooth ; upper valve depressed. 



In this species the proportions are reversed ; the length exceeding the 

 width. It is nearly of the same size as the former ; the beak is rather 

 more produced. 



Localities. Upper, and Lower chalk, near Brighton, and Lewes. 



78. Terebratula undata. Min. Conch. Tab. xv. fig. 7. 



Obovate, both valves convex, smooth ; front margin straight, with a 

 deep undulation on each side ; beak produced. 



