CARBONIFEROUS LABYRINTHODONT 565 
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 conspicuous 
dentinal tubuli, the ends of which terminate in the inward extensions 
of the peripheral layer. The secondary processes of adjacent 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 description 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 Schthyosaurus 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. 
Addenduim, 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 
vertebre and ribs from the Carboniferous formation ; but the vertebre 
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, [ 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 scen similar remains in the admirable 
collection of Dr. Rankin, of Carluke ; and, more recently, Mr. Russell 
has sent me up a number of vertebral bodies of different kinds from 
