VERTEBRATES. 21 



Fig. 1 represents the anterior face; la the outline of the base, upper side, 

 natural size. -> 9 y < 



Formation and locality: Keokuk limestone, Warsaw, Illinois. 



Cladodus micropus, N. and W. 



PI. 1, Figs. 2, 2a, 2b. 



Teeth of medium or small size, robust, higher than broad; 

 base small, shorter laterally than height of median cone, ellip- 

 tical, thick, rounded before and behind, and without anterior 

 sinus; principal cone robust, conical, strongly curved inward; 

 section lenticular throughout, with cutting edges; anterior and 

 posterior surfaces both, though unequally rounded, finely and 

 uniformly striated longitudinally ; lateral cusps 1-2 on either 

 side, very small, conical, acute, sometimes nearly obsolete. 



The teeth of this species are exceedingly abundant in the " fish beds" of the 

 Keokuk limestone in Illinois, and the collection contains a large number of 

 them. They exhibit considerable diversity of form, but have as common char- 

 acters their small elliptical bases, robust, recurved, ancipital, striated median 

 cusps and dwarfed or tubercular lateral denticles. Many of the specimens are 

 evidently beach-worn, and it is possible that their bases have been somewhat 

 diminished, and the lateral denticles truncated by the attrition to which they 

 have been subjected. 



There are no described teeth with which these will be likely to be confounded, 

 but they have much in common with two groups in the collection which have 

 been referred to species designated by the names of C. angulatus and C. robustus; 

 and though exhibiting marked differences, which are enumerated in the descrip- 

 tions of the above species, it is quite possible that all formed portions of the 

 dentition of a single species of fish. This is merely a conjecture, however, 

 which can only be confirmed or disproved by the aid of more material than is 

 now before us. 



Fig. 2, anterior face; 2a, side view; 2b, outline of base from above. 



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



