22 



They are the following : — 



Actinocyclus senarius Gallionella sulcata 



Ceratoneis Fasciola Navicula Entomon 



Coscinodiscus minor Tripodiscus Argus 



Patina Xanthidium furcatum 



radiatus hirsutum 



Dictyocha aculeata Zygoceros Rhombus 



Fibula Surirella 



Speculum And two new species of this genus. 



All the above, together with some well-known recent species of the 

 same extensive family of the Bacillarice, I have found in the sto- 

 machs of oysters. That they are not the detritus of chalk or chalk- 

 marl, although identical as to species with the fossils of the chalk, is 

 decided by the fact of my finding several of them alive ; and even in 

 the dead specimens there are the same distinct remains of ovaries and 

 other organic details, which enabled Ehrenberg to pronounce with 

 perfect accuracy that many similar dead forms had been recently in 

 a living state. If further proof be required, it may be furnished by 

 the process of charring, which immediately blackens the yellow 

 membranous integument of several of the species. 



We must not expect to find the same species of Infusoria in this 

 new locality during every period of the year. Like creatures of a 

 larger growth, oysters live on the food which is successively in sea- 

 son ; and I find, in point of fact, that even a different shore is marked 

 by a decided difference in the infusorial contents of the stomach. 

 The "Scotch Natives" are characterized at the present time, by innu- 

 merable minute circular forms, resembling the Coscinodiscus. Our 

 own oysters, on the contrary, are nearly destitute of these living rota- 

 tory disks, but they are much richer in more interesting species ; and 

 in addition to the siliceous-shelled Infusoria which are received into 

 their stomachs, they also occasionally furnish examples of calcareous 

 Polythalamia adhering to the inner surface of their shells. These lat- 

 ter microscopic cephalopods form part of the proper food of shrimps, 

 and accordingly I find that very minute Rotalia pass into the sto- 

 machs of shrimps entire. 



The comparison which Ehrenberg has conducted so successfully 

 between the chalk and recent Infusaria, I have attempted to extend 

 one step lower in the oolitic series, and to embrace in the investiga- 

 tion the Infusoria of the Kimmeridge clay. The large oyster beds 

 which occur in this stratum in my own locality, the vale of Ayles- 

 bury, very naturally invite the search for the food of these ancient 



