CERATODUS. 21 



studying the rich collection of the Bristol Museum I have found these difficulties very 

 real and troublesome. Other tests, such as the proportion of length to breadth, 

 convexity or concavity of grinding surface, have been tried, but with no great practical 

 success. Agassiz suggested that the flatter and broader forms may be palatal, and the 

 narrower teeth with more elevated horns mandibular, or vice versa. All such relative 

 tests are of uncertain value, until the species and their range of variation are well 

 known. 



A collection of fossil Ceratodus teeth from Maledi, Central India, 1 has suggested the 

 true key to this small but interesting problem. The Maledi teeth were in good preser- 

 vation, and certain of them showed recognisable fragments of attached bone. The 

 splenial buttress could be identified in some, 5 and a boss of bone, corresponding accu- 

 rately to that pedicle, which in the recent fish passes upwards from the palato-pterygoid 

 towards the frontal region, could be made out in others. 3 Further, as Dr. Oldham had 

 previously remarked, pairs of these teeth could in certain cases be fitted perfectly 

 together. It was plain that such teeth had been opposed, and had belonged, if not to 

 the same individual, at least to the same species. It is found that in all cases the teeth 

 recognised as palatal have one denticle more than the corresponding mandibular teeth, 

 while they are ordinarily somewhat broader and flatter. Of the fossils in the Bristol 

 Museum not a few have still attached to them bones precisely similar to those of the 

 mandibular teeth from Maledi. 4 These we may now take for mandibular teeth. They 

 have each four horns and no trace of a fifth. There is another group with a more or 

 less rudimentary fifth denticle, which differs also in having the first denticle of such form 

 that it could never have been received between two grinding surfaces. 5 These are plainly 

 palatal teeth. Again, teeth of the species C. runcinatus and Guliehni from the Mus- 

 cheikalk have more than once been found with attached bone. 6 Here also the 

 fossil palatal teeth are more or less perfectly five-horned, the mandibular four -horned. 

 There is therefore, so far as we know, a rule applicable to all the fossil species hitherto 

 described, making allowance for a few examples, probably exceptional individuals, which 

 have fewer than four horns. This rule may be stated thus : — The mandibular teeth are 

 slightly smaller and narrower than the palatal, with no more than four horns in the fossil 

 species. The first denticle is often prismatic, or adapted to two grinding surfaces. The 

 palatal teeth have, usually, in the fossil species either five horns, or four and a trace of a 

 fifth. 



The close association of Ceratodus with Lepidosiren and Protopterus is admitted by 

 all zoologists ; but it is not so universally conceded that the place of the three genera is 



1 See Dr. Oldham, "On some Fossil Fish Teeth of the Genus Ceratodus from Maledi, south of 

 Nagpur," ' Mem. Geol. Survey of India,' vol. i, p. 295 (1859); and Miall, "On the Genus Ceratodus, 

 •with special reference to the Fossil Teeth found at Maledi," ' Palseontologia Iudica ' (1877). 



- Plate V, fig. 115; PI. Ill, figs. 3 a, 3 b. 3 PI. V, fig. 12 b. Compare PL III, fig. 5 c. 



* PI. Ill, fig. 2. 5 PI. IV. G PI. Ill, figs. 4 a, 4 b (mandibular). 



