376 Davis — On the Fossil Fish of the Cretaceous Formations of Scandinavia. 



the largest row, fitting into the central groove of the opposing dentition, and on 

 either side the teeth of the lateral series become successively smaller.* 



Professor E. D. Cope f has discovered an interesting series of teeth in the 

 uppermost Cretaceous beds of Maria Farinha, which apparently occupies a position 

 intermediate between Ptychodus and the living ray, Myliobatis, and which he has 

 named Apocopodon. The teeth are covered with a thick layer of enamel, which 

 is ridged antero-posteriorly. The median teeth are shorter than Myliobatis, and 

 differ from both that genus and also Zygobatis in being exactly parallelogrammic 

 in outline, the extremities being truncated instead of angulated, as in those 

 genera. It may also be noted, that some of the Eocene Myliobatidae possess 

 teeth which approach more or less closely to the form of Ptychodus. A species 

 described by Leidy $ from the phosphate beds of North Carolina as Myliobatis 

 jugosus, may be taken as an illustration. Professor W. Dames § has also described 

 detached teeth from the Tuffkreide of Maastricht which appear to possess 

 characteristics indicating an intermediate position between Ptychodus and 

 Myliobatis, and so forming a sort of connecting link. The teeth are named by 

 Dames Rhomhodus linkhorsti. The occurrence of these intermediate forms in 

 various and widely separated parts of the world may indicate that the Ptychodonts 

 were the antecedent types of the MyliobatidaB ; and they certainly assist in 

 confirming the results of Smith Woodward's researches. 



Ptychodus decurrens, Agassiz. 

 (PI. XXXVIII., figs. 1, 2.) 



Dens piscis ostracionis. Bruckmann, F. E., 1752. "Acta. Phys. Med.," vol. ix., 



p. 116, pi. v., fig. 4. 

 Palate of unknown fish. Parkinson, J,, 1811. " Organic Remains," vol. iii., 



pi. XVIII., fig. 12. 

 Ptychodus decurrens. Agassiz, L., 1839. " Poiss. Foss.," vol. iii., p. 154, 



pi. XXV. J, figs. 1, 2, 4, 6-8 (nonS, 5). 

 Ptychodus decurrens. Owen, R., 1840-45. " Odontography," volume ii., 



pis. VIXII., XIX. 



* A. S. "Woodward, Proceedings of the Geological Association, vol. x.. p. 296. 1888. 

 t A contribution to the Vertebrate Palaeontology of Brazil, in Proc. Anier. Phil. Soc, vol. xxiii., 

 p. 2. 1886. 



J J. Leidy, Joum. Acad. Nat. Soi. Philadelphia, ser. 2, vol. viii., p. 240, pi. xxxi., figs. 4, 5. 1877. 

 § Sitzungsb. Ges. Naturf. Freunde, Berlin, pp. 1-3. 1881. 



