282 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuilC 1, 



described by me under the name Cestracion canaUculatiis in Mr. 

 Dixon's 'Geology of Sussex,' page 365. Mr. Catt's specimen 

 shows a dorsal spine and the vertebral column in conjunction with 

 the teeth ; and Mr, Potter's specimen shows the vertebral column 

 and two spines, that belonging to the second dorsal fin being straighter 

 and shorter than the anterior one. In commenting upon the probable 

 connexions of the teeth and fin-rays of the Placoid fishes, hitherto 

 discovered in the Carboniferous age, Prof. Agassiz conjectures that 

 Orodns should be assigned to Oracanthus, and Psammodiis to Ctena- 

 canthus. The occurrence, however, of the latter genus of Ichthyo- 

 dorulite in the coal-measures unassociated with teeth of the genus 

 Psammodus would militate against this suggestion. It is more likely 

 to have belonged to the genus Pcecilodus, which occurs in some 

 abundance in the Coal-measures as well as in the Carboniferous Lime- 

 stone of Bristol and Armagh. 



3. Oh the Structure of the Strata between the London Clay 

 and the Chalk in the London and Hampshire Tertiary 

 Systems. By Joseph Prestwich, Jun., Esq., F.R.S., F.G.S. 



Part II. — The Woolwich and Reading Series, 



[The publication of this paper is postponed.] 



June 1, 1853. 



Count Alexander von Keyserling and Prof. L. de Koninck were 

 elected Foreign Members. 



The following communications were read : — 



1. On ^Ae Southern Termination of the Erratic Tertiaries ; 

 and on the Remains of a Bed of Gravel on the Summit of 

 Clevedon Down, Somersetshire. By Joshua Trimmer, 



Esq., F.G.S. 



The present communication must be regarded as merely the open- 

 ing of a subject to which I would invite the attention of those who 

 have better opportunities of investigating it, — the search for traces 

 of the Erratic Tertiaries in districts which have hitherto been deemed 

 wholly free from them. 



The southern termination of these deposits, both on the eastern 

 and the western side of the island, is an interesting question involved at 

 present in much obscurity. Their termination on the East will be 



