4^ PALEONTOLOGY OF OHIO. 



When Conodonts were first found iu Ohio, I submitted them to Prof. 

 x\gassiz, who pronounced them the teeth of Selachians. 



Prof. E. S. Morse, one of the best living authorities on the structure of 

 invertebrate animals, to whom they wei'e referred as possibly the teeth of 

 naked mollusks, such as Doris, ^olis, etc., said that they bore a strong 

 resemblance to the teeth of mollusks, and might have belonged to the 

 progenitors of some of our living forms. 



The late Prof. Wm. Stimpson, one of our most learned and acciirate 

 zoologists, and one who had given special attention to the Crustacea, 

 after examining a lai-ge numljer of Conodonts, gave the opinion that 

 they might very well be the lingual teeth of mollusks, but they could not 

 have formed the dentition or spinous ai-mament of any Crustaceau. 



The Conodonts found by Prof. Pander were submitted by him to 

 chemical analysis, and he found them to be composed of carbonate of 

 lime. English chemists have found in them traces of phosphate of lime. 



Under the microscope they are shown to be composed throughout of 

 concentric layers of fine, structureless, but punctate tissue, not exactly like 

 that of the teeth of any living fishes; tliough their peculiarities of struc- 

 ture are not such as necessarily to exclude them from that class. 



It has also been suggested by some zoologists that these singular bodies 

 are the teeth of Cyclostomous fishes, and by others that they are dermal 

 ossicles. These different theories will be briefiy noticed in order. 



1. That the Conodonts were not the teeth of Selachians seems to me 

 almost certain, from their small size, their peculiar forms, and the homo- 

 geneity of theij' composition. In all known sharks the teeth are com- 

 posed of two distinct portions, the crown and the base. Of these the first 

 is the only part exposed, and it is formed of very dense tissue (den- 

 tine), traversed by radiating and ramifying canals, and is covered with 

 enamel. In the center is a pulp cavity, or less dense cancellated 

 tissue. 



The base is usually composed of rough, more or less porous, bone. This 

 is sunk in the integument and adheres to the cartilaginous jaw by strong 

 ligamentous attachment. The line of demarcation between the crown 

 and base is generally well marked, and when the teeth are fossilized, the 

 soft base has often perished, while the hard crown remains unchanged. 

 In the Conodonts, on the contrary, the crown and base are similar in 

 composition, or, rather, they have no base such as sharks' teeth exhibit. 

 From the form of their inferior margins we may infer that they were im- 

 planted in soft tissue, like the teeth of mollusks, the hooks of annelids, 

 etc., and were not set on jaws. 



2. Excluding the theory that they were the teetb of sharks, the range 

 of possibility in their affinities is still great. They may, as suggested 



