NO. 1699. ON EDESTU8 AND RELATED GENERA— HAY. 57 



formed. It will be seen, too, that the teeth change considerably as 

 they are followed from one end of the shaft to the other. In the 

 newer ones the downw^ard prolongations are pointed and carried for- 

 ward even to the extended axis of the fourth tooth in advance, while 

 in the smaller and older teeth the prolongations are truncated and 

 reach only the extended axis of the second tooth in advance. The 

 part of the shaft exposed is very narrow. 



5. DEFINITIONS OF THE GENERA. 



It is evident that Lissopnon is closely related to Helicoprion^ but 

 it is believed to be sufficiently distinct. It is possible that future 

 discoveries may abolish the differences noted. 



Edestvs. — Shaft straight or slightly bent, roots of the teeth be- 

 traying distinct traces of their original distinctness, and forming the 

 greater portion of the fossil. Blades of the teeth strongly denticu- 

 lated. Type, E. vorax Leidy. 



T 0X0 prion. — Shaft bent, but forming less than a complete coil, 

 mostly concealed under the bases of the teeth. Roots of teeth show- 

 ing no traces of their original distinctness in the shaft. Blades of 

 teeth high, pointed, feebly denticulated. Type, T. lecontei (Dean). 



Lisso prion. — Teeth and their shaft forming a spiral, the coils not 

 in contact. Roots of teeth indistinguishably consolidated. Shaft 

 widely exposed below the teeth. Inner border of shaft with a 

 longitudinal groove. Teeth high, the middle portion short, the 

 cutting edges smooth or feebly denticulated. Type, L. ferrieri Hay. 



HeUcoprion. — Teeth and shaft forming a spiral, the coils not in 

 contact. No traces of the separate roots of the teeth. Blades of teeth 

 distinctly denticulated. Little of the shaft exposed below the bases 

 of the teeth. A longitudinal groove along inner border, as in 

 Lissoprion. Middle portion of teeth variable; in the larger teeth 

 greatly developed. Type, H. hessonowi Karpinsky. 



6. THE NATURE OF THE OBJECTS CALLED EDESTUS, TOXOPRION, 

 LISSOPRION, AND HELICOPRION. 



In discussing this subject it is not necessary to enter into the his- 

 tory of opinions regarding the position occupied and the function 

 performed by the structures that have been described above. The 

 literature of the subject may be found cited in Doctor Eastman's 

 papers." In the first of these papers this author, who has devoted 

 so much attention to the fossil fishes and with such profit to science, 

 discusses the homology of the objects before us. He there frames a 

 strong argument in favor of regarding them as the consolidated 

 symphysial teeth of the lower jaws of sharks. Karpinsky had pre- 



«Bull. Mus. Comp. Zool., vol. 39, pp. 55-99, and in the Mark Anniversary 

 Volume, pp. 281-289. 



