2 Dr. A. S. AVoodwarcl on a Tooth o/Ceratodus 



The tootli of Ceratodus (PI. I. fig. 1) is firmly fixed to 

 a recognizable piece of the splenial bone, and is therefore 

 proved to belong to the left side of the lower jaw. It unfor- 

 tunately lacks the foremost denticle, but clearly agrees with 

 the majority of the Mesozoic teetii of Ceratodus in possessing 

 only four denticles altogether. It is thick and robust, with 

 the grinding-surface slightly convex, but wavy, and marked 

 by a very prominent coarse network of ridges (fig. 1). It is 

 specially remarkable for the long and narrow shape of its 

 crown, which is bounded on the inner side by a nearly straight 

 margin, not angulated opposite the second or third denticle. 

 So far as can be determined from a fragment, the foremost 

 denticle of the tooth appears to have been relatively large, 

 while the others rapidly decrease in size backwards. The 

 second and third denticles are sharply compressed to an acute 

 outer edge, and are separated by deep notches at the outer 

 margin (fig. 1 a), though not continued as conspicuous ridges 

 on the crown. Iheir long axes are not oblique, but directed 

 nearly at right angles to the inner margin. The fourth or 

 hindmost denticle is comparatively blunt. Fine horizontal 

 lines of growth are seen on the flattened inner (fig. \h) and 

 outer faces of the tootli. 



The specimen thus described differs from all the known 

 Mesozoic teeth of Ceratodus in its narrowness, combined with 

 the straightness of its inner margin and the direction of its 

 second and third denticles. Jn these respects, it is interesting 

 to observe, the tooth more nearly approaches that of the 

 existing Ctraiodus or JS'eoceratodus of Queensland (fig. 2), 

 and its only striking difference from the latter consists in its 

 having four denticles instead of six. The multiplication of 

 the denticles has already been observed in the teeth of certain 

 sharks as they are traced onwards in time * ; the same 

 ])henomenon obviously occurs in Ceratodus. 



There is, therefore, no doubt that the tooth from Cape 

 Patterson represents a new species, which may be named 

 Ceratodus avus. The fossil proves for the first time that the 

 remarkable Dipnoan genus to which it belongs had already 

 reached the Australian region so long ago as the early part of 

 the Jurassic period. At that epoch Ceratodus was still living 

 both in Europe j and in North America |, while it survived 



* A. S. "Woodward, " On the Palajontolopy of the Selachian Genus 

 Notuianus, Cuvier," Geol. Mag-. [3] vol. iii. (1880) p. '2o7. 



t Ceratodus PhiUipsi, Aga.<siz, ' Rech. I'oiss. Fosi^.' vol. iii. (18^=' 

 p. 13o, pi. xix. fig. 17 ; A. S. Woodward, Proc. Geol. Assoc, vol. 

 (1890) p. 202, pi. iii. fig. 5. 



X Ceratodus Uuenthcri, O. C. Marsh, Amer. Jouni. Sci. [3] vol. w. 

 (1878) p. 7(5, woodc. 



