4 PALEONTOLOGY OF OHIO. 



scapulas, thus giving us, as lias been said, nearly the entire bony 

 structure. 



Since tliis important discovery, Mr. Terrell has found a complete man- 

 dible and maxillary of larger size than any before met wi'Ji; the mandi- 

 ble being twenty-two inches in length. 



From this 2-ic-li array of material we get not only much additional light 

 in regard to the Bivnature oi Diniohthys, but are furnished w'lb the means 

 for accurately defining the two known species of the genus. It also shows 

 that some eiTors were committed, from confounding the two species, in 

 writing the descriptions contained in Yol. 1. 



When the njain portion of that volume was written, neither maxillary 

 nor mandible had been found on the Lake Shore, and all the bones of 

 Dinichthys collected at Shef&eld, Monroeville, and Delaware, had been 

 grouped together under one specific name. 



In a foot note appended to the description of Dinichthys on page 322 

 of Vol. I., Part II., is mentioned the discovery at Sheffield, by Prof. A. 

 A. Wright, of a mandible quite different from those found at Delaware. 

 This evidently belonged to a new species, to which the name Dinichthys 

 Terrelii was then attached. The large number of specimens since 

 obtained, and, indeed, all the remains of Dinichthys hitherto taken from 

 the summit of the Huron shale at Sheffield, belong, as we now know, to 

 this species, wliich is quite distinct from that found at the base of the 

 formation at Delaware. Hence the Dorsal plate figured on Plate 32, 

 the Cranium on Plate 33, and the Supra-scapulas on Plate 34, Vol. I., 

 should be credited to Dinichthys Terrelii rather than to D. Hertzei'i, 

 with wliich they were formerly and erroneously connected. The details 

 uf structure in which the species differ, will be given further on. 



The study of the specimens, the discovery of which has been described, 



■has resulted not only in a better knowledge of the anatomy of Dinichthys, 



but has revealed some interesting things in regard to the relations of this 



genus to living and fossil fishes ; all of which will be briefly referred to in 



the Images wliich follow. 



The most striking feature of Dinichthys, apart from its great size, is 

 its dentition, of which we have now all the parts. In this tlie most con- 

 spicuous elements are the massive mandibles, of which the posterior 

 extremities are rounded and flattened, and were evidently connected with 

 cartilaginous articular poi'tions. The anterior end of each mandible is 

 tuilied up to form a strong, acute, and prominent tooth. Behind this the 

 jaw is thickened by a ridge on the inside, which usually terminates above 

 in a triangular, tooth-like projection. The upper margin of the mandible, 

 for five or six inches behind this projection, is compressed, and consists of 

 remarkably dense, enamel-like bone. In D. Ilertzeri this is produced 



