156 



NEW YORK STATE MUSEUM 



By tabulating the differentials of these four species we shall in- 

 dicate the features in which D. dolbeli is unlike the rest. 





pleuroptyx 



stemmatus 



anchiops 



dolbeli 



Cephalon 



Short 



Longer 



Short 



Short 



Occipital ring 



No spine 



No spine 



Spine 



No spine 



Confluent papillae on 

 cheeks 



Conspicuous 



Inconspicuous 



Inconspicuous 



Inconspicuous 



Suture line on cheek 



Flush 



Flush 



Depressed 



Flush 



Pygidium 

 Lateral ribs 



11-13 



9-10 



8-9 



8-9 



Axial ribs 



i3-(i5) 



9-(n) 



9-0 4) 



10-O3) 



Ribs 



Deeply grooved, 

 rounded 



Not grooved, 

 rounded 



Not grooved, 

 rounded 



Faintly grooved, 

 rounded 



Caudal spine 



Short, acute, 

 elevated ax- 

 ially 



Broad, obtuse, 

 not elevated 

 axially 



Slender, extend- 

 ed, upturned, 

 not elevated 

 axially 



Broad, some- 

 what extend- 

 ed, upturned, 

 blunt, and 

 not elevated 

 axially 



Sharing its principal structures with the other three and sep- 

 arated from them by differentials which are of the same quality 

 as those distinguishing other members of the series, D, dolbeli 

 represents a notably early Devonic type of structure. 



Dimensions. Cephalon : large examples attain an axial length 

 of 40 mm and a width of 75 mm. Pygidium : an average example 

 has a length of 40 mm and a width of 60 mm. 



Lower Devonic. Grande Greve and Shiphead, P. O. 



Dalmanites lowi no v. 

 A very distinct type of structure is presented by a few pygidia 

 which are of considerable size, relativelv quite short, broad at the 



Dalmanites lowi 



top, with pleural ribs 10 or 11 in number, the last three of which 

 are simple and faint but all the rest very strongly duplicate through- 

 out their entire extent becoming obsolete at or just within the 

 margin. The axis is broad and the dorsal furrows rapidly approx- 



