248 



MOLLUSCA, BIIYOZOA, SPONGES. 



[Ch. XYII 



Fig. 2T9. 



Eadiolites Ifortoni, Mantell. llongliton, Sussex. "White chalk. 

 Diameter one-seventh nat. size. 

 Fig. 278. Two individuals deprived of their upper valves, adhering together. 

 279. Same seen from above. 



250. Transverse section of part of the wall of the shell, magnified to show the s;iacture. 



251. Vertical section of the same. 



On the side where the shell is thinnest, there is one external furrow and corresponding internal 

 ridge, a, h, figs. 278, 279 ; hut thev are usually less prominent than in these figures. Tiiis species 

 was first referred by Mantell to llippufites, afterwards to the genus Radiolites. I have never 

 seen the upper valve. The specimen above figured was discovered by the late Mr. Dixon. 



With these moUusca are associated many Biyozoa, such as Eschara 

 and EschariRa (figs. 282, 283), which are ahke marine, and, for the 



Fig, 282. 



EscJia) nut oceam. 



a. Natural size. 



&. Part of the same magnified. "White 

 chalk. 



EseJiara disUcha. 



a. Natural size. 



&. Portion magnified. 



"White chalk. 



Veiitric^iliies radiatus. 



Mantell. 

 Syn. OcelUiria radiata, 

 D"Orb. "White chalk. 



most part, indicative of a deep sea. These and other organic bodies, es- 

 pecially sponges, such as Ventriculites (fig. 284) and Siplionia (fig. 286), 



