THE UrPEK SILURIAN OF NORTH AMERICA. 



63 



ricana. Ends straight or concave. In other respects, in form and 

 in ornament, this species does not differ from the former. 



The abruptly truncate appearance of this species suggests the 

 probability that at least a rostral plate adjoined the cephalo-thoracic 

 shield, in which case it most likely possessed also marginal pieces. 

 Such a structure would bring it into close relation to Lankester's 

 Cyathaspis. 



Locality and horizon. As those of preceding species. 



Pig. 8. — Outline of Shield 0/ Palaeaspis bitruncata. (Nat. size.) 



Discussion. 



Dr. Woodward said he was glad the author had discovered the cana- 

 liculate layer in these fossils. Professor Lankester could not detect 

 it in the specimens examined by him. The oldest of these American 

 remains certainly appeared to be more ancient than any known in 

 Europe. He referred to the discovery by Dr. Lindstrom of the 

 remains of a Scorpion in beds of Upper-Ludlow age in Gotland 

 and stated that a specimen so similar as certainly to belong to the 

 same genus, if not to the same species, had been discovered at a 

 still earlier date in the Upper Ludlow of Lanarkshire by Dr. Hunter ; 

 although owing to the illness of Mr. Peach, to whom it was sent, 

 its occurrence had not been recorded. 



Professor T. Pupert Jones doubted if the older specimens described 

 by the author were as well defined as those of the upper beds, and 

 remarked upon the gap between the Wenlock and Ludlow beds 



