Dr. R. H. Traquair — A New Genus of Coccosteidce. 55 



the rocks to which they refer, and I challenge those who advocate 

 a Southern or a Midland origin for the pebbles to point to localities 

 within any probable distance where these rocks can be identified 

 in situ. 



Advocates of the former view must rest their whole case on the 

 supposed identity of a few pebbles with those of the Budleigh 

 Salterton conglomerate, and draw on their imagination for the home 

 of more than 99 per cent, of the materials. Those of the latter must 

 fly for refuge to. hypothetical rock-masses concealed from sight 

 beneath newer deposits. They, as it seems to me, will be driven to 

 adopt Mr. Mellard Reade's hypothesis of a marine origin for the 

 Bunter, because, as I have elsewhere pointed out, the rivers in this 

 central region would not be long enough or powerful enough to 

 round the pebbles. To them no doubt Mr. Mellard Reade's hypothesis 

 will be tempting ; but others, like myself, will wish to know how 

 it can be accommodated to known facts before we can transfer it 

 from the poetry to the prose of science. 



III. — On Phlyct^nivs, a New Genus of Coccosteid^;. 1 



By Dr. R. H. Traquair, F.R.S., F.G.S. 



(PLATE III.) 



IN the Geological Magazine for last month (January) I proposed 

 to establish the genus Pldyctcenius for the peculiar Coccostean 

 from the Lower Devonian beds of Campbelltown in Canada, 

 named by Whiteaves Coccosteus Acadicus. In this paper I 

 propose describing that form more in detail, along with an allied, 

 though at the same time very strongly marked species from the 

 Lower Old Red Sandstone of Herefordshire, to which on that occasion 

 I also referred. 



Mr. Whiteaves apparently did not recognize the extent of the 

 differences between this species and the true Coccosteus of the 

 Scottish Old Red ; but this I think he would have done, had he 

 succeeded more thoroughly in deciphering the arrangement of the 

 plates of the cranial buckler. As it is, he seems almost to hesitate 

 as to whether it is specifically distinct from Coccosteus cuspidatus 

 of Agassiz. "In some respects," he says, "the Campbelltown 

 Coccosteus very closely resembles the C. cuspidatus of Agassiz, but 

 in others there are such marked differences between the two forms 

 that it is thought more prudent, for the present, to distinguish the 

 Canadian species by a local name." He notices the similarity in 

 the arrangement of its " superficial " (i.e. sensory) grooves, with 

 those of C. decipiens, Ag., and finishes by saying : " It would seem, 

 therefore, that C. Acadicus may be distinguished from C. decipiens by 

 the different shape of the post-dorso-median plate, from C. cuspidatus 

 by the different arrangement of the grooves on the outer surface ot 

 its cranial shield, and from both by the peculiar sculpture of its 

 bony plates." 2 



y » Read before the Royal Physical Society of Edinburgh, 15th January, 1890. 

 "* 2 Trans. Roy. Soc. Can. vol. vi. sect. iv. 1889, p. 93. 



