268 PALAEONTOLOGY OF ILLINOIS. 



tial feature different from that of the teeth described above. These 

 large teeth are almost always much abraded, so that even so fine a 

 series as that obtained by Mr. Speingbe fails to afford a satisfactory 

 solution of their specific relations. Until recently they were regarded 

 as probably referable to G. deflexus, N. and W. ; but the explorations of 

 Mr Wachsmuth have brought to light in the lower Burlington fish- 

 beds a form which is unquestionably identical with the latter form — the 

 exact stratigraphic position of the originals of which was not known. 

 However, a comparison of them with the specimens discovered by Mr. 

 Wachsmuth affords almost conclusive proof that they were derived 

 from the same horizon. Their distinguishing characteristics, as com- 

 pared with the teeth above referred to from the upper Burlington hori- 

 zon, consists in the relatively stronger lateral denticles, the laterally 

 deflected principal cone, and the exceedingly delicate and crowded stria- 

 tum, possibly, also, the narrower postero-anterior diameter of the base 

 and the less prominent anterior basal angles and protuberances. 



In the absence of material in a perfect state of preservation, it is 

 impossible to determine the nature of the variations noticed above; and 

 however impressed we are with their probable specific' identity, the 

 material does not, as is the case with some of the Kinderhook forms, 

 exhibit all the phases of gradation which alone can furnish indubitable 

 evidence of such identity. Considering only the first described indi- 

 viduals, one cannot fail to appreciate certain intimate resemblances to 

 G. sygopus, N. and W. of the Chester; but taking into account the 

 ensemble presented by the teeth noticed above, there is little difficulty 

 in drawing the distinctive features of the species. We regret that our 

 means have not made it possible to present as fair a representation of 

 these teeth as of some of the other forms of this remarkable group. 



The Keokuk limestone has furnished a few fragmentary specimens 

 representative of a closely allied form, if not specifically identical with 

 that first described above; but of the latter we have only a few indi- 

 viduals, and these are not sufficient for a critical comparison necessary 

 to establish their relationship with the upper Burlington form. Closely 

 agreeing in shape and size, they are distinguishable by the much coarser 

 striation of the coronal cusps, there being not more than half the num- 

 ber of stria? usually observed in the present form. It is not improbable 

 these teeth constitute the remains of a form distinct from the above, in 

 which event we would suggest for them the specific designation C. 

 Keokuk. 



Position and locality : Not uncommon in the upper Burlington fish- 

 bed, Louisa and Des Moines counties, Iowa; Henderson, Warren and 

 Adams counties, Illinois. The Keokuk specimens are known to occur 

 at Hamilton, Illinois, Keokuk and Bentonsport, Iowa. 



