OF THE AMEEICAN PTERASPIDIAN, PAL^ASPIS. 559 



probably represent the fragments of the missing portion of the 

 dorsal shield, the hinder part of which was in all probability ridged 

 or fluted as the ventral shield, and therefore has been broken up 

 into the linear pieces which he has figured and imagined to be the 

 detached rings of a trilobite. 



X. Attempted Restoration of PALiEASPis. 



With regard to the attempted restoration in fig. 8 (p. 560), I do 

 not of course attach too much value to it as a whole. The fol- 

 lowing points may, however, be fully relied upon: — the form of the 

 dorsal shield, the total absence of a spine, the presence of orbital 

 notches, the singular striation at the mid-edge, and the nearly 

 straight lateral margin ; also the general form of the ventral shield, 

 the obtuse angle near but rather in front of the middle, the 

 truncate termination, and the general convexity. As to the 

 lateral plates, several specimens show the same form and position as 

 that represented in fig. 8 (p. 560) ; but it seemed unnecessary to 

 repeat the illustration. 



On the other hand, I am not quite certain regarding the exact 

 position of the ventral in relation to the dorsal shield. No specimen 

 yet found shows the two so perfectly as to enable me confidently to 

 adjust them to each other. Possibly the ventral plate lay farther 

 forward, but I incline towards the view that its actual position, if 

 not as represented, was somewhat farther backward. 



Of course, as Yon Alth has pointed out, the position of the 

 mouth represented by Lankester cannot now be accepted as correct. 

 It must be removed far enough forward to lie in front of the fore 

 edge of the ventral shield. But exactly how great a removal this 

 would mean is, in PalcBasj)is as in Pteraspis, at present uncertain. 

 In Yon Alth's specimen some slip has occurred. In mine the ends 

 are incomplete in both cases where the shields are together. I am 

 therefore uncertain whether or not the ventral plate fell short of, 

 or extended beyond, the dorsal backward. 



The exact form of its termination I have also been unable to 

 ascertain. Several specimens show a serrate edge at what appears 

 to be the hinder end of the ventral shield ; but these are fragments 

 showing only the internal face of the plate, and other specimens 



mit daran hangenden * Schuppen ' abgebildet. Dass die abgebildeten rhombischen 

 Gebilde Schuppen seien erscheint allerdings sebr wabrscheinlich ; weniger iiber- 

 zeugend wirkt die Abbildung bei der Frage, ob das daran hangende Schild- 

 fragment zu Pteraspis gehore." — Op. supra cit, p. 6. 



But the presence of the peculiar and fine striation on the fragment (which is 

 fortunately well preserved) of this unique and inTaluable specimen from 

 Herefordshire, to which Lankester calls special attention, should have been 

 amply sufficient to convince anyone of the Pteraspidian nature of the fossil 

 beyond all doubt or misgiving. 



Thus did Kunth narrowly miss the honour of first publishing the real nature 

 of the genus Scaphaspis, and its true relationship to Pteraspis and to Cyath- 

 aspis.^ 



