546 PROF. E. W. CLAYPOLE ON THE STRTJCTTJRE 



Against the new view originated by Kunth, and amended and 

 extended by Schmidt, Lanliester, in 1873, protested energetically.^ 

 In a short paper, in which he described a new genus, Holaspis, the 

 shield of which consists of a single plate, he asserted that in the 

 specimens described by Kunth the two shields were only in acci- 

 dental juxtaposition, and that the fossil could not therefore prove 

 anything in regard to their arrangement during life. He even 

 pushed his argument so far as to reason from analogy that, as 

 Holaspis was intermediate in structure between Cyathaspis and 

 JScaphaspis, it represented one term in a series of which Scaphaspis 

 was the simplest and Pteraspis the most complex form. There is 

 no reason for doubting that Holaspis is a new Pteraspidian, but 

 when this is granted it by no means follows logically that 

 Scaphaspis was its analogue. Differences had long been noted 

 between this last-named form and the rest of the group ; but these 

 had never been put into any definite shape before the appearance of 

 Kunth's paper. On examination of his figure it is, however, 

 impossible to agree with Lankester that the position of the shields 

 is accidental, or in any way to be compared with the packing of 

 shells one within another, which constantly occurs, says Lankester, 

 in Herefordshire and in Galicia, and, I may add, in Pennsylvania. 



Lankester's position is strong in defending the ichthyic nature of 

 Cyathaspis, and, consequently, of Scaphaspis, but it becomes weak 

 when he goes beyond this, and denies the co-existence of the two 

 as parts of the same animal. Altogether, judging from the 

 figures, Kunth's work deserved more consideration than it received 

 from Lankester. 



It is not necessary to do more than allude to the revival, by 

 Roemer and Eichwald, of Kner's original view of the cephalopodian 

 affinity of the Pteraspids, inasmuch as it was afterwards abandoned 

 by the former, and the specimen on which the latter relied is said 

 by Schmidt, who has seen it, and at Eichwald's request carefuUy 

 examined it, to be of quite different structure, and to belong to 

 some, at present undetermicable, but totally distinct group. 



IV. DiscovEEY OP DiPLASPis (Matthew) IN" Canada. 



Thus the matter remained for some years. No more illustrative 

 and critical specimens came to light in Europe, and the belief, if 

 such it could be called, in the ventral position of Scaphaspis rested 

 on the excellent but ill-interpreted example of Kunth. In 1885, 

 however, the writer published (as already mentioned) his descrip- 

 tion of the first Pteraspidian fishes that had been discovered in the 

 New World. Beyond adding a single new species, or, as was then 

 supposed, two new species, to the list of the family, these fossils 

 threw no additional light on the structure of the fishes. Dis- 

 missing this subject for more complete discussion in a subsequent 

 part of this paper, we will pass on to note the next contribution to 

 the history of the Pteraspids. 



Academy' for 1873, p. 11, and Geol. Mag. for 1873, pp. 190, 241, 478. 



