2 3 J: Proceedings of the Royal Physical Society. 



the course of the lateral-line grooves is clearly discernible, 

 wliile the form and arran^^ement of the constituent bones 

 may be pretty fairly made out, both by actual indications 

 of sutures as well as by radiating lines where the surface has 

 been abraded. It is clear also, from both specimens, that 

 these bones were quite fused or anchylosed together, and 

 in the cast now under description the sutures are sometimes 

 indicated by delicate raised lines as in P. Acadicus. I have 

 indicated in the sketch the course of the divisions between 

 the plates, naturally in a somewhat exaggerated manner, as 

 the lines themselves are only visible by a lens, and often 

 cannot be followed at all. But from what is seen it is quite 

 clear that the plates were similar in general form and 

 arrangement to those in P. Acadicus, and especially to those 

 in the specimen represented in Fig. 2, the median occipital 

 extending far forwards and the centrals being rather trun- 

 cated in front. 



One of the pencil outlines sent to me by Mr Smith 

 Woodward shows apparently the rostral or ethmoidal plate 

 in situ, thus completing the generic resemblance between the 

 Canadian and English species. 



We may therefore sum up the results of the preceding 

 investigations as follows : — 



Genus PhlyctcEnaspis, Traquair. Cranial shield more ovate 

 than in Coccosteus : constituent plates anchylosed, except the 

 ethmoidal ; median occipital elongated, pointed in front and 

 wedged in between the posterior ends of the oblong or ovate 

 central plates ; orbital excavation looking more anteriorly 

 than in Coccosteus ; course of main lateral-line groove nearly 

 straight from the external occipital to the post-orbital, where 

 it is very acutely bent backwards, l^lates of body-cuirass 

 imperfectly known. 



1. P. Acadicus, Whiteaves sp. External angle of cranial 

 shield divided by a shallow notch into two, the postero- 

 and antero-external angles ; surface ornamented by fine 

 tubercles, in most specimens showing a concentric arrange- 

 ment parallel to the margin of the constituent plates. 

 Lower Devonian, Canada. 



2. P. Anglicus, Traquair. Postero- and antero-external 



