part 1] dentition or climaxodus wisei. 5 



Climaxodus has been commonly regarded as identical with 

 Janassa ; but, if C. ivisei be correctly named, it is now clear that 

 the} 7 are two distinct genera. In the typically Lower Carboniferous 

 Climaxodus all the teeth seem to have been retained in the mouth 

 throughout life, while of the symphysial teeth only the apical edge 

 cm have been functional. In the typically Upper Permian 

 Janassa only a single transverse row of teeth was in function at 

 one time, the older transverse rows being thrust beneath to form a 

 supporting base ; while in all the teeth the corrugated hinder face 

 was extended, and must have been as useful for grinding as the 

 recurved apical edge for cutting. 



The dentition of Climaxodus wisei is especially remarkable for 

 the discrepancy in size between the foremost and the hindmost 

 teeth on the symphysis of the jaw, proving that there were only 

 about five or six teeth in succession during the greater part of the 

 life of the individual. Even the highly specialized Janassa bitu- 

 minosa is known to have had only seven or eight teeth in succession 

 from early youth to maturity. This is in marked contrast to the 

 •condition in all ordinary Elasmobranchs, in which the successional 

 teeth are very numerous and rapidly replaced — a condition as 

 evident in the- Palaeozoic Cladoselachidae, Pleuracanthidae, and 

 Edestidae as in the recent sharks and skates. The same limited 

 tooth-succession, however, is also to be observed in the Lower 

 Devonian Protodus, in the Carboniferous Cochliodonts, and perhaps 

 in the Carboniferous Psammodonts. It must, therefore, have been 

 a characteristic of many Palaeozoic Elasmobranchs, distinguishing 

 them sharply from those groups which survived until later times. 



Finally, most of the teeth of Climaxodus wisei are interesting 

 as exhibiting a restricted area of highly-vascular dentine much 

 resembling a tritor in the dental plate of an ordinary Chimaeroid. 

 A relationship between some of the Palaeozoic Cochliodonts and the 

 early Mesozoic Chimaeroids has already been remarked upon by 

 P. de M. Grey Egerton 1 and O. Jaekel. 2 The presence of an ap- 

 parently Chimaeroid character in Elasmobranch teeth Avhich are 

 noteworthy for their slow and scant}?- succession may, therefore, 

 have some special significance. 



EXPLANATION OF PLATE I. 



Eig, 1. Climaxodus u:isei, sp. nov. ; upper dentition, oral view, natural size. — 

 Calciferous Sandstone ; Calderside, near East Kilbride (Lanarkshire). 

 [Royal Scottish Museum, Edinburgh.] 



2. Do.; transverse row of three front teeth of the same jaw, oral (a) 



and anterior (b) views, three-halves of the natural size. 



3. Do. ; lower dentition of the same specimen, oral view, natural size. 



x = transverse row of three anterior teeth of the opposing- jaw (see 

 fig. 2). 



1 Q. J. G. S. vol. xxviii (1872) p. 236. 



3 Trachyacanthidge, O. Jaskel, Sitzungsb. Gesellsch. Naturf. Freunde, Berlin, 

 1890, p. 130; also ibid. 1891, p. 127. 



