DENDRODUS. 175 



the radiating lines described as medullary canals are, more probably, 

 sections of vertical fissures, or lamelliforra processes of the pulp, 

 radiating from the central body of the pulp to the periphery of the 

 tooth, and co-equal with the longitudinal extent of the tooth ; but 

 decreasing in number as the tooth contracts towards its apex. 



The species to which the tooth, exhibiting the beautiful and com- 

 plicated structure just described, belonged, may be indicated by the 

 name of Dendrodus biporcatus, in reference to the two opposite ridges 

 by which the tooth is characterized. 



Dendrodus strigatus. — A second and smaller tooth from the same 

 formation and locality, differs from the preceding in its more elongated 

 and slender conical form, with a nearly circular transverse section ; it 

 also differs in the absence of the two longitudinal ridges and in the pre- 

 sence of broader,deeper, and closer longitudinal impressions separated 

 by intervening convex ridges. As those characters strongly indicate 

 a specific difference in the animal to which it belonged, it may be 

 convenient to attach to this tooth the name of Dendrodus strigatus : its 

 microscopic structure, as shown by a fine transverse section, proves it 

 to be generically allied to the Dendrodus biporcatus. 



In the Dendrodus strigatus the central system of reticulate medul- 

 lary canals occupies a larger proportion of the mass of the tooth. 

 The radiated canals or processes of the pulp are shorter and more 

 branched : the systems of calcigerous tubes which diverge from the 

 numerous processes and branches are separated from each other by a 

 fine and clear line, and terminate in a broader band of calcigerous cells. 

 The appearances which the structure of the tooth thus presents in 

 the transverse section, somewhat resemble those of the tooth of a 

 Myliobates ; but the lobes or systems of calcigerous tubes are less 

 regular in form and size, 



Dendrodus hastatus. — The third tooth presents a more com- 

 pressed conical figure than the two preceding, and the opposite ridges 

 which characterized the Dendrodus biporcatus here form, as it were, 

 the margins of two cutting surfaces, and the opposite ends of the 

 flattened elliptical transverse section of the tooth. The length of 

 this tooth is eight lines, the longest diameter of its base three lines ; 

 the shortest diameter two lines. The tooth diminishes regularly from 



