FOSSIL FISHES. 61 



to distinguish it at a glance. The ridges are also broader and fewer in 

 number than in Ct. serratus, while the zigzag lines of the summit and 

 the vermicular ornamentation of the surface, pi'esent features that are 

 not found in any other known species. In most of the teeth of Ctenodus 

 the crown surface is smooth, and the acute denticles which crown the 

 ridges are highly polished. 



Formation and Locality : Coal Measures of Linton, Ohio. 



DiPTERUS ShEUWOODI (ll. Sp.). 

 Plate LVJIL, Figs. 17, 11 a, 17 5. 



Teeth one inch in length, triangular in outline; crown marked with 

 three prominent tuberculated ridges, separated by deep furrows somewhat 

 wider than the ridges. The strongest of these ridges forms one side of the 

 triangular tooth. On the angle opposite tliis side are a few irregular 

 tubercles but no traces of distinct ridges. Tlie denticles which crown the 

 ridges are somewhat compressed laterally, are rounded, smooth, and blunt 

 at the summit. 



This is apparently one of the upper palate teeth of a species of Dij)- 

 terns, and is specially interesting, as being the first relic of that genus 

 found on this continent. It can be readily distinguished from all the 

 species described abroad, by tlie small number of its radiating ridges. 

 This specimen is from the Catskill group of Tioga County, Pa., and was dis- 

 covered by my former assistant, Mr. Andrew Sherwood, now of the 

 Geological Corps of Pennsylvania, to whom I am indebted for an oppor- 

 tunity of examining it. 



In the same rock with this tooth are a number of imperfectly preserved 

 rliomboidal, or rounded scales, which are thick and strong, and have 

 tlie upper surface punctate precisely as in the scales of the foreign species 

 of Diptervs. Tlie surface of these scales was, probably, once highly pol- 

 ished, but like all the fish remains of the Catskill, the organic tissue seems 

 somewhat corroded. 



It is a singular fact, that while previous to last year, no teeth of Dipter- 

 ians had been found in this country, both Ctenodus and Dipterus were 

 almost simultaneously discovered; one in the Coal Measures of Ohio, the 

 other in the Catskill of Pennsylvania. More material is wanted for com- 

 paring the fishes which now Iteir the names of Ctenodus and Dlpterus^ 

 but, judging from the teeth alone, they might, with propriety, be included 

 in one genus. It is true that no scales have been found in the Coal Meas- 

 ures which could be referred to Ctenodus^ and it is quite possible that the 



