84 



PALAEONTOLOGY OF ILLINOIS. 



rounded ; sub-medial obtuse ridge traversing the crown longitu- 

 dinally, raised in the centre into a more or less prominent gib- 

 bosity. The upper side of this ridge is arched over transversely ; 

 on the lower side it descends into a broad and deep sulcus, 

 which runs the whole length of the crown, and occupies full 

 half the breadth. The surface of the ridge, and in worn speci- 

 mens, a part of the sulcus, is finely and uniformly punctate; 

 the lower margin of the crown is usually more or less corruga- 

 ted or striated vertically, sometimes showing faint traces of 

 marginal plications; root small, oblique, and has usually dis- 

 appeared. 



This species bears considerable resemblance to some of the specimens figured 

 by Agassiz, under the name of Selodus turgidus, but is narrower and more dis- 

 tinctly striated. This species is represented in the collection by a large number 

 of specimens, in which the characters enumerated in the above description are 

 quite constant. 



Figures 16, 16 a are top and side views of a specimen, of medium size. 



Formation and locality : Keokuk limestone, near Warsaw, Illinois. 



Genus EDESTUS, Leidy. 



\ 



Gen. Char. — Maxillary bone segmented, segments beveled 

 anteriorly and excavated posteriorly for co-adaptation. Teeth 

 in form resembling those of Carcliarodon ; one co-ossified with 

 each maxillary segment. 



Edestus minor, Newb. 



PI. IV, Fig. 24. 



Teeth relatively small, 10 lines long, 5i lines wide at base, 

 3 lines thick, set saddle-like upon the edge of a flat, bony jaw, 

 conical in outline, acute, margins sharp, coarsely doubly crenu- 

 lated; sides laterally arched, giving a lenticular section to the 

 tooth; surface smooth and highly polished. 





