T32 NEW YORK STATE MUSEUM 



that D. p 11 s t u 1 o s u s does not occur in the rocks of New York State, 

 nor, so far as known, in any district eastward of Kentuckx , uiiiil \ cr)- late in 

 the Devonic (Oneonta beds); whereas in the ]\Iississipi)i xallc)- region 

 it is tolerably abundant throughout the Mesodevonic. Its advent, then, in 

 the Hamilton limestone of the central western states, is probably to be 

 explained through immigration by way of Manitoba and Canada from 

 Europe. 



The arrangement of dermal plates in the head shield of this species is 

 shown in the accompanying text figure 25, and adjoining it is placed, for 



sake of comparison, one showing the cranial roof of Neoceratodus. Making 

 proper allowance for the fact that the preorbital plates remain cartilaginous 

 in the recent form, and that the anterior median element ("dermal meseth- 

 moid") is undivided, as it is also in Macropetalichthys, the correspondence 

 in pattern will be sufficiently obvious. The significance of these resem- 

 blances can hardly fail to be appreciated, after attention has once been fixed 

 upon them, and they are considered in connection with other points f)f 

 agreement throughout the entire skeleton. We need not dwell upon these 

 matters further here than to say that all available evidence goes to show 



