14 PALEONTOLOGY OF OHIO. 



titcs and Binichthys are the same ; the only differei)ce being that in 

 Heterostius this bone is ranch shorter than broad, while in Binichthys 

 the two diameters are nearly equal. 



The craninm of Biniclithys seems also to apj^roach more nearly in 

 structure to those of Asterolepis and Heterostius than to that of Coccos- 

 teus. The resemblance would also seem to be somewhat closer with 

 Heterostius than with Asterolejjis. In the latter genus the occipital por- 

 tion of the cranium forms nearly a straight, transverse line, while in 

 Heterostius it is very much arched, as in Binichthys. The posterior 

 margin of the supra-occipital plate — which forms the center of the arcli — 

 has nearly the same chai'acter in Binichthys and Heterostius, that is, it is 

 impressed with two deep pits separated by a narrow ridge, and behind 

 these is a peculiar pyramidal projection. All the bones of the hinder 

 part of the head in Binichthys are usnally found soldered lirmly together, 

 the union between the Supra-occipital and tlie Epiotics being so firm that 

 their points of junction cannot be discerned, and they seem to form one 

 solid bone. This bone is, however, sometimes found disarticulated, and 

 it is figured on Plate LIX. 



The anterior portion of the head is generally dismembered, and seems 

 to have consisted of strong bony plates lined with and move or less firmly 

 united by cartilage, as in Heterostius and Asterolej)is. 



The outer surfaces of the external bones of Binichthys are marked with 

 a fine granular, almost imperceptible ornamentation. In addition to this, 

 the cranial surface is inscribed with a series of excavated lines which form 

 an ornamental pattern, of which the outlines have not yet been fully 

 made out. Something of the sort is discernible on the crania of nearly all 

 the Placoderms. It may also be seen on the Post-Temporals (" Supra- 

 Scapulas "), and in Binichthys and Coccosteiis traces of it are visible on the 

 bones of the plastron. 



There is this m.arked difference, however, between Binichthys and its 

 congeners, Asterolepis, Heterostius, Ooccosteus, Pterichthys, Aspidich- 

 thys, etc., that they all have the surfaces of their external plates orna- 

 mented with thickly-set and often prominent and stellate tubercles, while 

 the surface bones of Dinichthys show only the granulation and linear fur- 

 rows referred to above. 



In one instance the anterior part of the head has been found entire, but 

 this was in a concretion, and it was so much injured by the removal of its 

 hard and tough matrix, that the outlines of the plates composing it can- 

 not be discerned. This shows, however, that a sheet of bone covered the 

 entire surface of the head. In all the crania found at Sheffield, the muz- 

 zle has disappeared ; only the occipital and central portions remaining. 

 The brain-box was apparently partly bone and part cartilage ; as we find, 



