Fossil Teeth o/Myliobatis. 43 



figured by Bucldand in his ' Bridgewater Treatise,' was 

 selected by Agassiz as the type of this species, and described 

 as noteworthy for its superficial striation and the relatively 

 considerable breadth of the median plates. The latter are 

 shown to be six times as broad as long, and almost invariably 

 exhibit a greater or less amount of antero-posterior curvature. 

 The teeth of the first lateral series are somewhat longer than 

 broad, though both these and those of the second series are 

 not so elongate as in M. Dixoni. The coronal contour is fliat 

 in the adult, as shown in the accompanying woodcut (fig. 2), 

 and almost so in the young. 



Fig.2. 



The following specimens of lower teeth seem to represent 

 successive stages in the dentition of this specific type, and 

 five (nos. I., 11., IV., VI., IX.) are shown in PI. I. figs. 5- 

 9. Nos. IX. to XI. are unusually large, and may be cer- 

 tainly regarded as pertaining to overgrown individuals, 

 although the last was described by Dixon as the type of a 

 new species, M. irregularis. 



Lower Dentition o/" Alyliobatis striatus. 



In the same series also we may evidently place the speci- 

 men figured by Dixon as M. Edwardsii (B. M. no. 25615), 

 which is intermediate in size between nos. III. and IV., and 

 has similar relative proportions. This fossil is very much 

 abraded, and thus not so satisfactory as coidd be wished -, 

 but, like several others, it appears only to difi'er from the 



