130 GREY CHALK MARL. 



"obliquely ovate, with an angle at the beaks, the deeper valve having 

 radiating undulations, with numerous minute aculei ; these are sometimes 

 wanting. The other valve is for the most part externally concave, with- 

 out undulations, but bearing sharp hollow spines with their points pressed 

 close to the surface, and often hooked. The surface that received the 

 semi-external cartilage, is sometimes very distinct, extending transversely 

 upon the beaks, so as almost to form ears *," 



Tab. xxvi. figs. 13. 17, agree in many respects with the above descrip- 

 tion : the shell is very thin, and the spines closely pressed to the surface. 



fig. 16, is more convex than the preceding, has but few 



spines, and possesses a lamellated structure. Some specimens of this kind 

 are nearly orbicular, almost destitute of spines, and frequently exceed 

 1 -5 inch in width and length ; these probably belong to another species. 



Localities. Hamsey, Stoneham ; mutilated specimens are very 

 common. 



59. Terebratula suhrotimda. Min. Conch. Tab. xv. figs. 1, 2. 

 Subrotund, somewhat depressed, smooth, valves equally convex, beaks 



short. 



This and the following species are abundant in the chalkf, but of rare 

 occurrence in the marl ; they are so common, that a particular description 

 is unnecessary. 



Localities. Hamsey, Eastbourne. 



60. Terebratula subundata. Min. Conch. Tab. xv. fig. 7. 

 Subovate, somewhat depressed, smooth ; valves equally gibbous, margin 



depressed in front, with two lateral undulations. 

 Localities. Hamsey, Eastbourne. 



61. Terebratula sulcata. 



Depressed, transversely ovate, with diverging longitudinal furrows', 

 upper valve convex, lower valve depressed anteriorly ; front of the 

 depressions straight, plicated, with an imdulation on each side ; beak small, 

 margin serrated. 



* Min. Conch. Vol. iii. page 80. f Vide Chalk Fossils, No. 76. 



