I903-1 Hay, North American Cretaceous Fishes. 69 



difference found in the form of the bases of the two fangs of a 

 specimen of E. petrosus. As regards the cross-section at the 

 middle of the tooth, I find no considerable difference. The 

 specimen labelled "£. pressidens" agrees with the descrip- 

 tion of that species, but the " E. ferox" also has the inner 

 face considerably more convex than the outer, and the sec- 

 tions of these faces may be regarded as forming two sides 

 of a triangle, with the separating angle rounded off. The 

 grooves bounding the cutting edges of "E. pressidens" are 

 hardly apparent, while there are indications of them in the 

 specimen called E. ferox. Doubtless there were individual 

 variations in this character. 



If Loomis's explanation of the manner of replacement of 

 the palatine fangs is correct, as it quite certainly is, we can 

 see why in some cases the palatine bone projects beyond the 

 base of the fang, while in other cases the fang projects beyond 

 the bone. After the new tooth has taken its position in front 

 of the old tooth and at the very extremity of the palatine bone, 

 the latter proceeds to extend itself forward in order to provide 

 a seat for the base of the next tooth in succession. Thus we 

 sometimes get a palatine bone in one stage, sometimes in 

 another. In the "ferox" specimen the palatine had extended 

 considerably in front of the fang; in the ''pressidens" speci- 

 men the fang had only recently taken its place. 



The specimen called E. pressidens is a little more than one- 

 half the size of that called E. ferox, the tooth being 32 mm. 

 long, that of E. ferox 51 mm. The palatine bone of the 

 "pressidens" is also relatively slenderer than the other; but 

 all these differences are probably due to difference in age of 

 the animals. 



E. ferox appears to differ from E. petrosus in three respects. 

 The inner face of the palatine fang is smooth, while in E. 

 petrosus it is coarsely striated. In E. ferox the cutting edges 

 of the palatine fang are minutely serrated; in E. petrosus 

 they are smooth. In both species there is, on the outside of 

 the palatine, a broad shallow groove which runs from the 

 lower hinder portion of the bone upward and forward. In 

 E. ferox this groove meets the upper edge of the bone over 



