544 Professor H. O. 8eeley — On Ceratodus. 



third or hindermost denticle the width is 2-1 cm., exclusive of the 

 base; but including the base, the transverse hinder measurement 

 is 3-1 cm. The three wedges which form the external mai'gin 

 diminish in size successivel}'- from front to back. The notch between 

 the first two is almost exactly a right angle, and the notch between 

 the second and third is rather less than a right angle. The thickness 

 of the dental plate, including the base, is 1-8 cm., but above the base 



Left Dental Plate of Ceratodus Kannemeyeri. Natural size. 



it is about 1-3 cm. thick. The sides of the notches which define the 

 denticles are flat, smooth, and so formed that the notch extends 

 a little inward as it ineets the nearly horizontal crushing surface; 

 and the flat sides converge outward to form the sharp external angles 

 of the wedges, which round convexly along the crest of each on to 

 the flat surface of the plate. 



The tubuli of the dental plate are vertical in all parts of the 

 tooth, and are arranged in linear series, so that they form labyrinthic 

 patterns, which have a general extension in the longitudinal axis of 

 the tooth and extend transversely across the three external denticles, 

 but are parallel to the external margin of the posterior rounded 

 convexity, which is rather more elevated than other parts of the 

 tooth. It is probable that this pattern is exposed by removal of 

 the enamel. . 



The fossil resembles C. Guilielmi (Plien), from the Muschelkalk 

 of Hoheneck, in form of the dental plate and its flatness, and in 

 character of the denticles ; but differs in having only three 

 denticulations, with terminal convexities back and front. It also 

 may be compared with C. Eislopianus from the Gondwana beds of 

 Nagpur, in the thickness of the dental plate, which involves some 

 resemblance in the denticles ; but in that Indian species there are 

 five denticles instead of three, and the plate is relatively narrower. 

 There is no species with a similar broad flat crushing surface, and 

 three thick wedge-shaped denticles, which decrease in size from 

 front to back. 



