626 GEOLOGY OF OHIO. 



viz., the "jugulars" and the "post jugulars" or "hyoids," really belong to 

 the ventral armor, the supposed hyoids being identical with the anterior 

 ^ entrals, but with their points turned in the opposite direction, and the 

 "jugulars" being the missing posterior ventrals. This arrangement of 

 the plates brings out new points of harmony between the two placo-gan- 

 oids Dinichthys and Coccosteus. 



In connection with the figures now published it may be well to 

 allude to one point. The outer margins of the anterior ventrals are 

 seen to be "rabbeted" for a considerable part of their length, as if for 

 the reception of the margin of some contiguous plate. No plate, how- 

 ever, has yet been brought to light which could occupy this position. 



It may be of assistance to future students of Dinichthys to give the 

 measurements, and therefore the relative size, of various bones which 

 are known to have belonged to one individual specimen of D. Terrelli a 

 specimen of moderate size, found upon the east branch of the Vermillion 

 river by Mr. Jay Terrell. 



Cranium, length, median line, 15| inches. 



width, flattened, with suborbital, 24 inches. 



width between supra-clavicular joints, 16 inches. 



back of supra- occipital to center of eye-orbit, Vl\. 

 Suborbital, length 17 J inches, width 6 inches. 



back extension from center of orbit, 12 inches. 

 Supra-occipital, vertical thickness, 2£ inches. 

 Premaxillary, width of tooth, 3 inches, height 5J inches. 



width, with prong, 4}. 

 Mandible, length, 14J inches, height, tooth, 5J inches. 



length of posterior ramus 7\ inches, width 3| inches. 

 Maxillary, length 4| inches, width 3J inches. 

 Dorsal shield, length 13 inches, with neck, 19 inches. 



width 17 inches. 

 Posterior ventrals, ( "jugulars "), length 16 inches, width 7 inchea. 

 Anterior ventrals, width 5 inches, length 16Jinches. ;.' 



