32 OLD RED SANDSTONE FISHES. 



2. Pteraspis rostratus, Agassiz. PI. IV, figs. 1, 2, 3, 7, 8 ; PI. V, fig. 4; PL VI, 



figs. 1, 2, 3, 6, 10 ; and PI. VII, figs. 3, 5, 9, 

 12, 13, 16, 17, 19. 



Cephalaspisrostratus, Agassiz. Poiss. foss., vol. ii, p. 148, pi. 15, figs. 5, 6, 183.5. 

 Pteraspis rostratus, Huxley. Quart. Journ. Geol. Soc, vol. xvii, p. 165, wood- 

 cut, 1860. 

 ' — — Lankester. Brit. Assoc. Report, Trans. Sect., p. 58, 1864. 



Derivation. — Rostratus, bearing a rostrum. 



Characters. — Scutum grandius et minus attenuatum quara in Pt. Crouchii ; rostrum 

 cuneiforme, discus elongatus, quadrangularis lateribus parallelis, spina magna, cornua 

 lateralia angularia; rostri superficies superior striis undosis, antice ciirvatis, parallelis 

 ornata; superficies externa disci et partium orbitalium striis concentricis ornata. 



StratigrapMcal Position. — Lower Old Red Sandstone (Cornstones). 



History. — This species is more common than the last, and appears to be the one 

 which was known to Prof. Agassiz. Prof. Huxley gave a restoration of its outline^ in 

 1860. Agassiz's type specimen is drawn in PI. IV, fig. 2. 



General Remarks. — This is a larger species than Pt. Crouchii, sometimes attaining a 

 length of four inches and a half from the tip of the rostrum to the termination of the 

 disc. It differs from Pt. Crouchii in the shape of its rostrum, which is broader at its 

 termination and shorter relatively than in that species, — in the shape of its disc, which is 

 that of a parallelogram with the anterior angles rounded off, — in the shape of its cornua, 

 which are thicker and stronger in Pt. Crouchii, — in the relative length of its spine, which 

 is less deeply inserted in the disc. It is by no means uncommon to get specimens of 

 this species with all the parts adherent. The rostrum does not readily break off as 

 in Pt. Crouchii ; and, not being proportionately so large nor upwardly curved, it is more 

 frequently preserved, and knocked out of the stone with the rest of the shield ; indeed, 

 it is rare to see a specimen of Pt. rostratus in which all the parts are not attached, 

 though still rarer to see one in which they are not to a large extent inextricably 

 imbedded in the dense Cornstone. The markings of the inner surface of the disc 

 consist of two straight ridges on each side passing obliquely forwards from the region of 

 two small oblong depressions situated on either side of the median line, a little posterior 

 to the centre of the shield, and of a broad anterior elevation in the median line, corre- 

 sponding with a similarly broad depression of the outer surface. Two curved lines, 

 similar to those in Pt. Crouchii are noticeable in some specimens ; but they are not so 

 constant or so sharply marked as in that species. The striations on the outer surface are 



^ The very obscure cornua were not quite correct in this outline (nor in that which I gave in the 

 'Quart. Journ. Geol. Soc.,' vol. xx, p. 194, pi. xii, fig. 10); but in all other respects the restoration 

 was most valuable. 



