334 PALEONTOLOGY OF ILLINOIS. 



face occupied by relatively strong, sharp vertical costse, which iu the 

 opposite face are much less strongly marked. 



The very few specimens of the present form indicate considerable 

 individual variableness, and which, it is interesting to note, is precisely 

 of the nature observed in other forms of the group, as in that cited in 

 connection with 8. cheiriformis, wherein in one or other, or both, of the 

 rows the cusps present the appearance of arrested growth near the mid- 

 dle of the tooth, thence continued by disproportionately large cusps. 

 So far as refers to the coronal elements there is much similarity to the 

 form described above under the name 8. Mcristatus, though the rows 

 diverge more rapidly posteriorly, in which respect they recall a pair of 

 the rows in the form 8. cheiriformis, as also in the shape of the cusps, 

 the costation of which, however, is stronger. 



Position and localities : All. the above described forms occur in the 

 fish-bed of the Upper Burlington limestone, intermingled with the 

 various other remains of fishes peculiar to this horizon; BuffiDgton 

 creek, Burlingtou and Augusta, Iowa, the former locality affording the 

 majority of the specimens, and all those, with a single exception, 

 employed iu the illustrations. 



The Keokuk limestone has afforded a few examples of the present 

 group of teeth, but the specimens, unfortunately, are in so imperfect 

 a state of preservation as scarcely to permit of satisfactory compari- 

 son with the Upper Burlington forms. There occur amongst these 

 specimens apparently the same varieties as noticed in the preced- 

 ing descriptions, though the teeth resembling S. cheiriformis are most 

 common. But the Keokuk specimens of the latter type seem to have 

 the cusps more erect and arranged in three or four rows, and the basal 

 region would appear to. be shallower. It is, therefore, very probable 

 that a suit of well-preserved specimens of these teeth would show dis- 

 tinctions of specific value. The cheiriform examples are labeled *S'. 

 Keokuk. All the Keokuk specimens are from the vicinity of Warsaw, 

 Illinois, Keokuk and Bentonsport, Iowa. 



Stemjiatodtjs compactus, St. J. and W. 



PI. 8, Kg. 38, a, b, c. 



Tooth very small, robust, long-elliptical in outline viewed' from above. 

 Base deep, lateral walls slightly converging in their descent, laterally 

 compressed iu front and produced downward into a process, posterior 

 extremity rounded, inferior surface moderately excavated and forming 

 less than half the antero-posterior diameter of the entire tooth. Coro- 

 nal region moderately produced laterally, though the longer axis extends 

 autero-posteriorly, and occupied by a single median row of depressed 



