36 Proceedings of the Royal Physical Society. 



synonyms of Asterolepis, Eichw., along with Pterichthys, Ag., 

 and many other names. 



However, the dorsal plate figured later on by Eichwald 

 (2, pi. Ivi., fig. 3) as belonging to his P. orncUics, not only 

 stamps it as Asterolepid, but leads us also to suspect that it 

 is generically different both from Asterolepis and Pterichthys, 

 and that this is the case was clearly shown by Lahusen (11). 

 Describing a head with a portion of the body attached, as 

 well as the two median dorsal plates and some other frag- 

 ments of the body and arms of a species to which he gave 

 the name of P. Panderi, Lahusen pointed out, first that the 

 course of the cephalic furrows (lateral line system) was not 

 the same as in Asterolepis ; second, that the postmedian plate 

 was different in shape ; third, that there was no os terminale ; 

 fourth, that the articular plates of the arms were longer. But 

 when he speaks of the arms being more simple in structure 

 than those of Asterolepis, and we compare his figures, it is 

 quite clear that he had before him only the proximal segment 

 of the limb; and it must also be noted that in some cases he 

 regards the grooves of the cephalic lateral line system as 

 sutures, or at least as former sutures, and so very considerably 

 increases the number of bones which he allots to the cranial 

 shield. 



Trautschold's contribution to the structure of Pothriolepis, 

 published shortly afterwards (12), consists largely of correc- 

 tions of Lahusen's paper in matters of detail. He also formu- 

 lates the differences between the heads of Pothriolepis and 

 Asterolepis, laying stress on much the same points as Lahusen, 

 but adding that the angular and opercular elements (Pander) 

 found in the latter are wanting in the former genus, though, 

 strangely enough, the angular is represented in the diagram 

 wliich he gives of the head in Pothriolepis. JSToteworthy it is 

 that he mentions having found in one specimen a lid or cover 

 to the " orbit," and accurately fitting it. As regards the 

 arms, of which he had no complete specimens, he pointed out 

 certain differences in the arrano-ement of their constituent 

 plates, and considers it doubtful whether the limb was divided 

 into proximal and distal portions, as in Asterolepis. 



The discovery by the officers of the Canadian Geological 



