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NEW YORK STATE MUSEUM 



that D. pustulosus does not occur in the rocks of New York State, 

 nor, so far as known, in any district eastward of Kentucky, until very late in 

 the Devonic (Oneonta beds) ; whereas in the Mississippi valley 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 



Fig. 25 Dinichthys pustulosus Eastm. Middle Devonic; Iowa. Restoration of the head shield, dorsal aspect, xf^. 

 C^ central i £0 = external occipital ; jl/=- marginal ; MO = median occipital ; P = pineal ; PO = preorbital ; PtO= postor 

 bital ; Ji ^ rostral, sometimes identified as nasal or mesethmoid. Sensory canals represented by double dotted lines. 



Fig. 26 Neoceratodus forsteri (Krefft). Dorsal aspect of cranial roof, drawn as if flattened out to same extent as in 

 Dinichthys. Cartilaginous portions dotted, and dermal plates lettered to correspond with those of Arthrodires. The undivided, 

 anterior median plate is commonly termed mesethmoid. xj^ 



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 of 

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

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



