150 
Terrelli, after Mr. J. Terrell, who has secured the finest series 
of specimens. 
This genus of gigantic bony-cased fishes has heretofore 
been represented only by the species D. Hertzert, Newb., dis- 
covered and procured with great pains by the Rev. Mr. 
Hertzer, a Methodist missionary at Delaware, Ohio. Many 
specimens of this species have now been obtained, and the 
characters of its enormous jaws and massive shield-like plates 
are well known. They all occur near the base of the Huron 
shale of Ohio, corresponding to the upper Hamilton of New 
York, or more precisely, the Genesee shale. 
Plates and fragments of jaws have more recently been 
found at a horizon near the top of the Huron shale, at Shef- 
field, Ohio, indicating for the species a length of some 10 to 
15 feet. A cranium two feet across was obtained by Mr. 
Terrell, which rivals in size that of the older species. Subse- 
quently, the discovery of perfect jaws has shown beyond 
doubt that the Sheffield species is distinct. These jaws are a 
foot and a half long, somewhat less than those of J. Hertzer7 ; 
but their chief difference lies in the fact that instead of having 
a series of small teeth or denticles set along the front portion 
of the side, as is the case in the other, their edges are raised 
into a sharp, cutting blade—the maxillary and pre-maxillary 
shutting down upon the mandible like scissors. These and 
other differences afford ample grounds for regarding the - 
species as new. 
Quite recently, almost the entire bony structure of a large 
individual of Dinichthys Terrellimthe new species—has been 
found by Mr. Terrell, in the Huron shale near Avon Point, 
Lorain County, Ohio. In this specimen, the median plate of 
of the back has a diameter of 80 inches, measured over the 
arch, and weighs 80 pounds; the cranium is two feet wide at 
its posterior extremity; the fins are composed of strong bony 
rays as large as a man’s little finger. 
This interesting series of bones has been purchased for the 
cabinet of the School of Mines of Columbia College, where 
nearly all the remains of Dinichthys yet found are now centered. 
The genus Dinichthys, which is thus shown to have ranged 
through probably the entire period of the Huron shale, be- 
longs to the group of placoderm ganoids, which are eminent- 
ly Devonian forms; it is most nearly allied to the little 
Coccosteus and Pterichthys, which Hugh Miller has made so 
familiar, from the Old Red sandstone of Scotland. But the 
largest of these fishes was not longer than an average-sized 
mandible of the giant Dinichthys. 
