NO. 1699. ON EDE8TU8 AND RELATED GENERA— HAY. 45 



The body of the fossil is made up of a shaft of vasodentine, dense 

 and rough on the surface and without enamel. As has been shown by 

 other observers, in the case of other species of the genus, this shaft 

 consists of trough-shaped processes, one of which runs forward from 

 each tooth, and which supports and partly incloses the process of the 

 preceding tooth and is supported and partly inclosed by the succeed- 

 ing one. The photograph (pi. 12, fig. 1) shows the grooves limiting 

 each of these processes above and below. It will be seen that measur- 

 ing each process, or sheath, from the hinder end of the tooth which it 

 supports to its anterior end, the first one is 84 mm. long, the second 

 105 mm., the third 125 mm., the fourth 138 mm., the fifth 149 mm., 

 the sixth 158 mm. This means that the anterior end of each sheath 

 receded from the end of the shaft by considerably less than the 

 length of the tooth to which it belonged. 



This species appears to differ from E. heinrichii in various j^articu- 

 lars, some of which will be mentioned. 



1. The form of the shaft is different in the two species. In E. 

 cremdatus the greatest height is in front of the middle of the length 

 and under the second tooth; in E. heinriclin it is behind the middle 

 and under the fourth tooth. It is possible that in the original of the 

 figures of the last of these" the last-formed tooth is missing, but 

 allowance for this would put the greatest height at the middle of the 

 shaft. The shaft of E. crenidatus is relatively pointed in front; that 

 of E. heinrichii is deep and truncated. If in the figured specimen of 

 E. heinrichii the last-formed tooth is missing, a portion of its enamel 

 ought to show under the last one present. If no tooth is missing, the 

 shaft terminated in quite a different manner from that of E. crenu- 

 lafvs. Furthermore, in case the last-formed tooth of that specimen 

 of E. heinrichii is missing there would have been present 9 teeth ; in 

 the type of E. crenidatus there are only 6. The type of E. heinrichii 

 is a considerably larger specimen (280 mm. long) than that of E. 

 crenulatus. It is difficult to see how the latter could become modified 

 so as to resemble the former. 



2. It will be noted the last sheath of E. crenidatus extends much 

 farther forAvard than does that of E. heinrichii; also, it covers rela- 

 tively less of the depth of the shaft. 



3. In E. crenulatus a tongue-like process of the unenameled surface 

 of the shaft runs backward between each tooth and the pointed 

 process of enamel of the next tooth behind until it touches this hinder 

 tooth ; in E. heinrichii the tongue-like process is cut off from the 

 hinder tooth by a prolongation of the anterior one. 



4. The teeth of the two species are of different forms. In E. crenu- 

 latus the angle between the two lines carried from the apex of the 



"Geol. Surv. 111., vol. 4, pi. 1, fig. 1; Aun.,N. Y, Acad. Sci., vol. 4, pi. 5, fig. 2. 



