Structure and Classification of the Asterolepida}. 37 



Survey of numerous well-preserved entire specimens of 

 Bothriolejns in the Upper Devonian rocks of Scanmenac Bay- 

 enabled Mr Whitoaves to give a description (13, 14, 15), 

 accompanied by excellent figures, of a new species of the 

 genus, to which he gave the name of Pterichtltys {Bothriolepis) 

 canadensis. These specimens are certainly the finest examples 

 of Asterolepid remains yet discovered, and clearly show all 

 the salient features of Bothriolepis in a manner never before 

 exhibited. Unfortunately, Mr Whiteaves does not seem to 

 have had complete access to the literature of the subject, as 

 he makes no reference to the papers of Egerton and Beyrich 

 on Ftcrichthys, or to those of Lahusen and Trautschold on 

 Bothriolepis, and consequently does not seem to be aware 

 that the identity of Asterolepis, Eichwald and Pander, and 

 Pterichthys, Agassiz, had ever been questioned, or that very 

 tangible differences between Bothriolepis and Aster olepis had 

 been already pointed out ; for, as regards the former, he says, 

 " It is still open to question, however, whether the genus 

 Bothriolepis is or is not a valid one, and sufficiently distinct 

 from Pterichthys" (15, p. 106). 



However, he bases his reference of the Canadian species to 

 Bothriolepis on the sculpture of the plates, pointing out some 

 discrepancies in the plates of the head compared with those 

 in Pander's restoration of '' Pterichthys" (=:iAsterolepis) ; and 

 noticing the absence of a tail, he contents himself with saying, 

 " It seems therefore highly probable that Bothriolepis will 

 prove to be distinct from Pterichthys proper." Even as 

 regards the species, he seems to be in doubt as to whether or 

 not it is distinct from B. ornatus of Eichwald. 



But if the generic distinctions between Asterolepis and 

 Pterichthys are but slight, nothing can be more salient than 

 those which distinguish Bothriolepis from both, as will be 

 seen from the following sketch : — 



Head. — The median occipital (m. occ, PI. II., Fig. 6) 

 has its lateral margins more perpendicular to the posterior 

 one, the anterior margin shows not merely a shallow re- 

 entering angle for the postmedian plate, but a deep semi- 

 elliptical notch or excavation. The postmedian is small, 

 narrow, semi-elliptical in shape, and, except its anterior 



