DF,VONIC FISHES OF THE NEW YORK FORMATIONS I31 



fine tuberculation, wavy suture lines, and more Coccosteuslike aspect. 

 Lower dental plates -with a simple trenchant margin, behind which there is 

 an abrupt downward slope beset with rudimentary denticles. Shear teeth 

 with convex functional margin, simply trenchant, and without posterior 

 denticles so far as known. Vomerine teeth resembling those of D. inter- 

 m e d i u s. Visceral surface of occipital region without prominent ridges, 

 the posterior pit of the median occipital scarcely divided. Pineal plate 

 apparently in contact with centrals, and with inconspicuous foramen. 



Of this species, which appears to have been rather abundant and widely 

 distributed in the Mesodevonic of this country, nearly the entire dermal 

 armor is known, and the whole of the dentition. Amongst the primitive 

 characteristics of the form in question may be reckoned its fine, Coccosteus- 

 like tuberculation, sinuous suture lines, remnants of an original denticulation 

 along the sloping posterior margin of the lower dental plates, and the com- 

 paratively slight development in the latter of a toothlike projection at no 

 great distance behind the symphysial beaks. At the same time, however, 

 it must be acknowledged that this species marks a considerable advance 

 over typical Coccosteuslike conditions, inasmuch as the functional margin 

 of the dental plates is no longer serrated, the dorsomedian plate has 

 a strongly developed inferior carina and posterior process, being also 

 emarginate in front, and a clavicular occurs of the usual Dinichthyid type. 



The occurrence of D. pustulosus in the Black slate of Kentucky, 

 a horizon corresponding approximately to the Genesee of New York State, 

 favers the supposition that it was the immediate progenitor of forms like 

 D. intermedius and D. terrelli of the Cleveland shale, which have 

 retained a similar form of dentition. According to this view, D. herzeri 

 and other species in which the functional margin of the dental plates is 

 denticulated, form a separate series, descended along collateral lines from 

 Coccosteus, and characterized by the persistence of this distinctly Cocco- 

 steuslike feature. We should therefore be inclined to look upon D. hal- 

 modeus as standing in the same ancestral relations to the type species of 

 this genus as does D. pustulosus to D. terrelli. It is noteworthy 



