244 NORTH STAFFORDSHIRE COAL FOSSILS. 



consist of " two dental plates with a flat undulated and punc- 

 tated surface, and with five or six sharp prongs on the outer 

 side." It has two similar dental plates in the lower jaw 

 It is also described as having in the front part of the 

 upper jaw " two obliquely-placed incisor-like dental lamellae 

 which have no corresponding teeth in the lower jaw.' 

 (See "Nature," 18/1.) In the British Museum there are 

 several specimens of Ctenodi, one of which shows a large 

 portion of a skull with both the upper teeth and one lower 

 tooth in situ. From a careful examination of these, as well 

 as of a large number of specimens in our own collection, 

 it would appear that the teeth of fishes of this genus 

 vary much in individuals. No specimen has yet been 

 described having the whole of the dental series complete, 

 nor, so far as we know, has a specimen been found sufficiently 

 perfect to enable us to determine whether or not Ctenodus 

 was furnished with a tooth in the front part of the mouth. 

 The close resemblance between this genus and its modern 

 representative would lead us to infer that a similar additional 

 tooth existed in the latter genus. This surmise, together 

 with many other peculiarities, can only be satisfactorily 

 cleared up by the discovery of more perfect specimens. 



Ctenodus cristatus, Agassiz. (Ref., Poiss. Foss., vol. iii., 

 pi. 19, fig. 16.) The teeth known by this name are of two 

 kinds, mandibular and palatal. The palatal teeth are com- 

 posed of a thin plate somewhat elliptical in form, varying 

 from two inches to two and a half inches in length, and 

 from an inch and a half to an inch and three quarters in 

 breadth. The upper surface of the plate is concave, and 

 is covered with a number of close-set transverse ridges, 

 the grooves between the ridges becoming deeper as they 

 approach the outer margin of the tooth. The summit of 

 the ridges is " studded from end to end with closely- 



