YEETEBRATES. 277 



tbread-like stria?, which are more numerous and crowded in the basal 

 region in front, but sparser and somewhat irregularly implanted above, 

 and extending two-thirds or three-fourths the distance to the acute apex, 

 with a rather wide plain space parallel with either edge and reaching 

 half way towards the base; upon either extremity there are apparently 

 but two lateral denticles, of which the exterior pair are relatively strong, 

 snbcircular in section, or less compressed than the median cone, very 

 slightly deflected laterally, more strongly recurved than the median 

 cusp, and similarly finely striated; the inner pair of denticles are less 

 than half the size of the outer ones, similar in shape and slightly 

 advanced in the basal border above the anteroinferior angles. A large • 

 sized tooth measures in hight.30 inch, hight of outer denticles .12, 

 lateral diameter of base .34, anteroposterior diameter about . 12. The 

 smaller teeth distinguishable are, perhaps, half the dimensions of that 

 above measured. 



The preservation of the specimen under consideration is such as not 

 to afford a distinct knowledge of all the details — the shale in which the 

 specimen is imbedded so closely adhering as to necessitate the most 

 careful and laborious manipulation in developing the specimen, which, 

 we regret, we have not had the opportunity to perform. But the gen- 

 eral features, as exhibited by the teeth, may be satisfactorily ascer- 

 tained, and these would appear to indicate less individual variableness 

 than obtains in some species which have been determined from isolated 

 teeth. Minute speck-like bodies are associated with the mass, which 

 possibly represent portions of the shagreen, since they present a much 

 more uneven or papilious surface than observed in the surface of the 

 cartilage itself. 



We have long had in our possession a little tooth from the Middle Coal 

 Measuresof Iowa, which we have come to regard after careful comparison 

 as identical with the above described teeth, with the smallest of which 

 it agrees in size. The basal region in front, however, is more strongly 

 arched downward in the middle and relatively deeper ; but the coronal 

 cusps in number and ornamentation apparently present no marked fea- 

 ture by which it is distinguishable from the typical examples associated 

 upon the jaws described above. 



It is our intention eventually to give this interesting specimen a more 

 careful study than it is possible at the present time to bestow upon it. 

 And, in connection with some fragmentary jaws discovered by Prof. 

 "vVorthen in the St. Louis formation, which we believe to be the first 

 veritable examples of their kind found in American Carboniferous 

 deposits, if not indeed elsewhere, we hope to obtain more definite 

 knowledge of their systematic relations in the great class of which they 

 are among the earliest representatives. 



