FOSSIL FISHES. 57 



become so decidedly arched in subsequent stages of growth, as the latter 

 spines are. As it is now generally believed that the spines of Ortliacan- 

 thus were worn by the sharks of which the teeth are called Dijjlodus ; 

 and as at least two species of Diplodtis are found at Linton, it is liighly 

 probable that the curved and straight spines were associated respectively 

 with these different teeth. When found in connection with the teeth so 

 as to fix the relationship between them, the names now given to these 

 spines may be suppressed. Until such relationship shall be determined, 

 however, it will serve a nseful purpose to describe them under distinct 

 names. 



Formation and Locality : Coal Measures, Linton, Ohio. 



Genus GYRACANTHUS, Agass. 



Since the publication of the descriptions of the species of Gyracanthus 

 found in Ohio (Yol. I., Part II., p. 330), I have received a letter from Mr. 

 D. Honeyman, of Halifax, in which it is stated that the great spine figured 

 by Prof. Dawson (Acadian Geology, 2d Edition, p. 210), and named by 

 him Gyr acanthus magnificus, was taken by Mr. Honeyman from the 

 Louver Carboniferous limestone of Baddeck, Cape Breton, and not from 

 the Coal Measures, as I inferred from Prof. Dawson's notes. This case, 

 therefore, instead of forming an exception to the rule to wdn'ch I have 

 referred, viz., that the spines of Gyracanthus, while common in the Coal 

 Measures of Europe, in America have only yet been found in Lower 

 Carboniferous rocks, affords another illustration of it. We should not be 

 justified in saying that GyracantJms did not exist in America during the 

 Coal Measure Epoch, for it may be any day found in the coal strata ; l)ut it 

 is an interesting fact that, up to the present time, no traces of it have been 

 seen in this country in other than Lower Carboniferous rocks. 



In letters received from Sir Philip Egerton since the publication of my 

 notes on Gyracanthus, it is stated that it has been demonstrated that many 

 of the spines of Gyracanthus found in Europe were attached to the pec- 

 toral fins, and that some of these are much worn, as though by contact with 

 the bottom of the sea in which this shark lived. 



These facts are cited by Sir Philip Egerton as confirmatory of the view 

 presented in my notes, that the spines of Mac] mr acanthus belonged to 

 the pectoral fins. 



