Structure add Classi/ic:itio)i of the Asterolepidie. 29 



Next, as to the anterior ventro-lateral plate itself and the 

 mode of articulation of the arms. Notwithstanding the con- 

 trary opinion of Hu;ih IMiller and j\rCoy, Sir Philip Egerton 

 strongly maintained that the arms were articulated to sepa- 

 rate " thoracic " phates, marked off by a distinct line of suture 

 from the anterior ventro-lateral ; and so confident was he in 

 this opinion, that he went so far as to say that he was " at a 

 loss to conceive liow Professor Pander can have been led to 

 assign the attachment of the arms to the ventro-lateral plates 

 as shown on the magnified figure on tab. vi. of his magnifi- 

 cent work on the Devonian fishes, although in the preceding 

 plate these organs are correctly drawn as appended to the 

 thoracic plate" (9, p. 105). Now in this matter Pander's 

 accuracy cannot be impugned as far as Asterolejns is con- 

 cerned, for the Ptussian plates of this genus were found 

 isolated and uncompressed, and the place of articulation of 

 the arm can easily be verified on a specimen of the anterior 

 ventro-lateral plate of A. ornatus in the British Museum 

 collection. And as regards Sir Philip's appeal to Pander s 

 figs. 5 and 9 on tab. v. of his work, in which the "thoracic" 

 plates seem to be represented in specimens of Pterichthys 

 from Lethen, he could not surely have read the author's 

 explanation of these figures, in which it is expressly stated 

 that this appearance is due to fracture ! 



Nevertheless, accepting Pander's description of these parts 

 to hold good for Asterolepis and Egerton's for Pterichthys, 

 Beyrich (10), Lahusen (11), and Zittel (16) have sought 

 herein to fi^nd a diagnostic mark between the two genera ; 

 but this idea I cannot corroborate. Careful study of a laige 

 series of Scottish examples of Pterichthys has convinced me 

 beyond all doubt that Egerton was in error on this pointy and 

 that his '' thoracic " plates are simply parts of the anterior 

 ventro-laterals, separated not by a suture, but by an internally 

 projecting ridge, which, in crushed and decorticated speci- 

 mens, gives the false impression of a division. I may add 

 that the species macrocephalus, in connection with which Sir 

 Philip expressed his opinion so strongly, is not a Pterichthys, 

 but a Bothriolepis, and that isolated plates of the larger species 

 of the same genus demonstrate absolutely the unity of the 



