302 TRANSACTIONS OF THE [MAR. 15, 



from behind forward ; crowns triangular, conical, compressed, 

 obtuse, smooth, in anterior and largest tooth crown about half 

 an inch long and high, two-fifths of an inch wide, teeth of first 

 lateral series broader than high, crown four-fifths of an inch wide 

 b3' half an inch high, elliptical in outline, rising into a central 

 cone or boss, which is obtuse, smooth and, like the central 

 series, uniformly pvmctate and jet black ; second lateral series 

 compressed from front to rear, one inch or more in breadth, 

 crown bearing an obtuse cone near the interior end. 



The teeth of this group appareutl}' form symphysial rows on 

 the jaws of some Cochliodont fish of which the broader lateral 

 teeth are unknown or have not yet been connected with them. 

 Probably the dentition was similar to that of GocJiliodus nobilis, 

 described and figured in Yol. II. of the Geological Report of Il- 

 linois, pp. 88, PI. YI., YII. and YIII. Doubtless some future 

 discovery will show the general characters of the dentition more 

 fully and permit of the association of these central teeth with the 

 lateral ones ; until this shall be done, however, it will be neces- 

 saiy to designate the central teeth by a provisional name, such 

 as is now given to them. 



Formation and locality, Keokuk limestone, Keokuk, Iowa, 

 where the fine series of teeth represented in PL XXIY., fig. 24, 

 was discovered by Mr. L. A. Cox, to whom the species is dedi- 

 cated. Types in the cabinet of Mr. William F. E. Gurley. 



Ctenodus fleisheri, n. sp. 

 PL XXIY., fig. 25. 



Upper palate teeth triangular in outline, concave, the crown 

 traversed by five rows of rounded, obtuse tubercles which are 

 traceable to the apex of the triangle. Here mere lines of dots 

 represent the diminished tubercles. 



Only one tooth of this species has j-et been found and 

 that is imperfect, but its characters are sufficiently well pre- 

 served to show that it is specifically distinct. The radia- 

 ting rows of the tubercles which traverse the surface of the 

 crown are not unlike those of Ctenodus jlahelliformis of the 

 Chemung, but are less crowded and the tooth is larger than any 

 specimen of that species yet known. So too the character of the 

 tuberculation recalls that of Heliod us Lesleyi from the Chemung 

 and it is evident that during the time of the deposition of the 

 Chemung and Catskill rocks a group of Dipnoan fishes inhabited 

 the waters of eastern North America which were closely related 

 one with another and j-et quite distinct from any of their con- 

 geners inhabiting other parts of the world. Whatever peculiari- 



