6 24 GEOLOGY OF OHIO. 



admit of the presence of the ventro-medianplate.which was not preserved. 

 The margins of the overlapping area, both on the right and left sides, are 

 so entirely coincident, that no one on seeing the specimens can doubt thai 

 the two were related to each other 'as shown. 



The bones numbered 5 and 6, belonging to another individual, con- 

 stitute a third case in which there is a perfect fit in the overlapping. 

 Whether these two belong to the same species as the other four is a 

 matter of no moment so far as the relationship of the bones is concerned. 

 The three cases taken together make an array of fact which must be 

 conceded to be conclusive. The only alternative would be that each fish 

 carried somewhere upon his armor a pair of bones other than the ante- 

 rior ventrals, which nevertheless had the same shape and size of tip as the 

 anterior ventrals, and which therefore would fit into the excavations upon 

 the "jugulars." I have already quoted Dr. Newberry's description of his 

 supposed "post jugulars" and "hyoid" bones which overlapped the "jug- 

 ulars." It will be seen that the description corresponds almost completely 

 with that of the perfect anterior ventrals which I am now able to figure. 

 ■If he had procured perfect specimens of the "post-jugulars," I feel confi- 

 dent that he would have figured them with the "jugulars" in the Mono- 

 graph. And as his published figures of the anterior ventrals lacked the 

 triangular tips which fit upon the "jugulars," we must assume that his 

 material failed to show him the identity of his "post-jugulars" and "an- 

 terior ventrals." 



III. Since the so called "jugulars " and the anterior ventrals were 

 companion bones, the question arises whether these four plates (together 

 with the narrow median plate) covered the jugular or the pectoral 

 or the ventral portion of the fish. The preponderance of evidence 

 to my mind is in favor of placing them in the ventral position, the "jugu- 

 lars" becoming the posterior ventrals with their arched outlines pointing 

 backward. 



I am not aware that any individual specimen has yet been found with 

 the bones so completely in place as to settle this question. There are 

 some difficulties in the way of the view which is taken, to which refer- 

 ence will be made later. But there are a number of weighty considerations 

 in favor of it. In the first place the so called "jugulars" are pretty large 

 for service as jugulars. They are longer than the mandibles. In the spe- 

 cimen from which figures 3 and 4 were taken (a fish of which eighteen 

 bones were preserved together), the mandibles were fourteen and a half 

 inchesin length while the "jugulars" are sixteen, measured either from 

 tip to tip or around the arched border. Fig. 6 is 22| inches long, while a 

 plate of the general shape of Fig. 4 has been discovered near Columbus, 

 as I am informed by Professor Claypole, who has kindly sent me a tracing 

 of it, which was at least 30 inches in length. They would thus seem to be 

 somewhat large for filling the "space between the mandibles," while upon 

 he belly there was room for considerable expansion. 



