BUFFALO SOCIETY OF NATURAL SCIENCES 99 



the Ptyctodont tritors which are almost always found in the same 

 rocks. This opinion, even if substantiated by the finding of Acan- 

 thaspis plates and Ptyctodont tritors in association, would not in 

 our view militate against referring Acanthaspis to the Arthrodira, but 

 be another link in the chain of evidence tending to prove that the 

 Ptyctodonts are themselves Arthrodires, though with a specialized 

 dentition. 



In the Buffalo Museum there are two specimens of Acanthaspis that 

 add somewhat to our knowledge of this form. One consists of two 

 ventral plates, the right and left of one individual, on a block of lime- 

 stone. Another is a plate with an attached spine in which the cross- 



FiG. 34. Acanthaspis armata Newberry. Restored Outline of Specimen 

 Shown in Figitre 33 



section of the spine is clearly shown. This is elliptical, and proves that 

 the spine was not as compressed as might be thought from its attach- 

 ment to so thin a plate. 



Acanthaspis armata Newberry 



E 1857 Block of limestone bearing right and left antero-ventro- 

 laterals with their attached spines. (Text-figs. 2>3> 34-) 

 There is also a fragmentary indeterminable plate on the 

 same block. The specimens are shown in inner view; 

 the suture between each plate and its attached spine 

 cannot be made out. In one spot an impression shows 

 the ornamentation of the outer face; this consists of the 

 characteristic ornamentation of this species. 



