10 PALAEONTOLOGY OF OHIO. 



as described and figured by Pander and Owen, consists of six pieces ; the 

 central rhomboidal plate (" ventro-median ") being detaclied from the 



VENTRAi Shield of Dinicdthys Terrelli, N. 



One-tenth natural size. 



triangular plate which forms the middle of the anterior margin (" pre- 

 ventro-median "). In Dlnichthys, these two bones, having almost exactly 

 the same form, are united by a narrow bony band. It is almost certain 

 also that they were connected in Coccosteiis, though it is possible that the 

 isthmus that united them was cartilaginous. The union of these bones is 

 plainly seen in Pander's figures ( TJeber die Placodermen des Devonischen 

 Systems. Taf. 5, Fig. 1, No. 13.) 



The anterior pair of lateral plates {pi^e-ventro-laterals of Owen) are 

 relatively longer and narrower in Dinichthys than in Coccosteus, and their 

 anteridr angles are more prominent; but these differences are of trifling 

 import. The anterior margin of these plates, as well as that of the pre- 

 veiitro-median is strongly reflexed. This character is indicated by a 

 double line, and is common to the plastrons of both the genera under 

 consideration. 



The posterior lateral plates {post-ventro-later'ols of Owen) are broader 



