Structure and Classification of the Asterolepidae. 23 



increase of weight in the skeleton of the head is compensated 

 for by a great increase in the thickness of the blubber, so as 

 to produce the bull-formed head which Captain JJavid Gray 

 has figured as characteristic of an aged male. 



The period of the year (March) when the carcase of this 

 animal was obtained by the fishermen is not without interest. 

 As a rule Hyperooclon rostratus is cauglit on our coasts, or those 

 of the north-west part of continental Europe, in the autumn, 

 when the animal is making its annual migration from tlie 

 Arctic Ocean to the south. Lilljeborg relates ^ that a female 

 was stranded at Landskrona, in Sweden, in April 1823 ; but 

 this aged male from Shetland is the only specimen which 

 has been obtained as early as the month of March. Captain 

 David Gray, however, states ^ that on the voyage northwards 

 in the month of March, immediately after leaving the Shet- 

 land Isles, these whales are occasionally met with. Probably 

 at that season they are migrating to the Arctic Ocean. 



IV. On the Structure and Classification of the Asterolepidie. 

 By Dr E. H. Traquair, F.R.S., F.G.S. [Plates I., II.] 



(Read 21st November 1888.) 



Of this remarkable and problematic group of Palaeozoic 

 Yertebrata, the genera w4th which I propose to deal in the 

 present communication are Aster olepis, Eichwald, Pterichihys, 

 Agassiz, Bothriolepis, Eichw., and Microhrachius, Traq. We 

 shall commence with 



Pterichthys, Agassiz, 1840. 



( = Asterolepis, Pander, pars, non Eichw. , nou H. Miller. ) 



The structure of Pterichthys, sadly misunderstood by 

 Agassiz, was more satisfactorily discussed by Egerton (8) ; 

 but the writer who in former times knew most about it was 

 Hugh Miller. It is, indeed, strange that though Miller 

 published in 1841 (3) wonderfully accurate figures both of 

 its upper and under surfaces, Agassiz should have mistaken 

 the belly for the back, and should have given in his " Old 



^ Memoir, translated in Royal Society's publications, p. 247. 

 '■^ Proe. Zool. Soc, London, December 19, 1882. 



