62 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 3, 



towards the centre of the tooth, between every pair of primary pro- 

 longations of the pulp-cavity. The short secondary processes which 

 are sent out from opposite sides of the primary prolongations of the 

 pulp-cavity, give off in the same way, from their ends, pencils of con- 

 spicuous dentinal tubuli, the ends of which terminate in the inward 

 extensions of the peripheral layer. The secondary processes of ad- 

 jacent primary prolongations alternate and, as it were, interlock 

 with one another, so that the inward extension of the peripheral 

 layer takes a sinuous course between them. A thin layer of dense 

 and glassy enamel invests the tooth continuously, but sends no 

 processes into its interior ; and, of course, under these circumstances 

 there can be no cement in the interior of the tooth, nor can its surface 

 be said to be plaited or folded. It will be understood that this de- 

 scription gives merely the principle of arrangement of the parts of the 

 tooth : its details could only be made intelligible by elaborate figures. 

 In Rhizodus and in Ichthyosaurus the principle of construction of 

 the complex tooth is totally different, the surface of the tooth being 

 really folded, and prolongations of the cement being continued into 

 the folds. 



Addendum, January 14, 1863. 



The Referee, to whom the preceding description of the skull of 

 Anthracosaurus was sent, has suggested that it is desirable I should 

 express some opinion respecting the systematic relations and affinities 

 of the fossil. I am glad that I am in a far better position to comply 

 with this suggestion now, than I was when the description of the 

 cranium was sent to the Society ; for at that time I was not in 

 possession of the valuable evidence regarding the characters of the 

 vertebral column, which has come into my hands within the last 

 few days through the exertions of my indefatigable correspondent, 

 Mr. Russell. 



For some years past, I have been acquainted with well-ossified 

 vertebrae and ribs from the Carboniferous formation ; but the ver- 

 tebrae have always been devoid of their arches and processes ; and 

 though the ribs presented characters suggestive of their belonging to 

 a higher division of the Vertebrata than Fishes, I thought it better 

 to wait for further evidence as to their real nature before giving any 

 account of them. 



More than a year ago, I brought away with me from the collection 

 of the Earl of Enniskillen, at Florence Court, a remarkable rib and 

 vertebral centrum. I have seen similar remains in the admirable 

 collection of Dr. Rankin, of Carluke ; and, more recently, Mr. Rus- 

 sell has sent me up a number of vertebral bodies of different kinds 

 from the Airdrie workings. I had every reason to believe some of 

 these vertebrae to belong to Anthracosaurus, and it was with that 

 conviction in my mind that I ventured to caution the members of 

 the Geological Society, on the occasion of the reading of Mr. Marsh's 

 paper on " Eosaurus Acadianus"* against too hastily concluding that 

 the vertebral centra, which he had found in the Nova-Scotian coal- 



* See ante, p. 52. 



