PLATE IV. 



Fig. 



1. Pteraspis rostratus. A fine specimen, showing the concave surface of the shield. 



Observe the pit between rostrum and disc, the elevation into a ridge of the 

 fused margins of these two parts, and the long ridges of the disc. Cradley, 

 Herefordshire. In the author's cabinet. 



2. Agassiz's type specimen of C. rostratus. The hollow character of the cornua is 



well seen in the fractured cornu of the left side. Whitbach, Herefordshire. Sir 

 R. I. Murchison. Poiss. Poss. Tab. 1 a, fig. 6. 



3. Pt. rostratus. A specimen showing well the form of the rostrum, and its relation. 



to the anterior margin of the disc. Cradley. Author's cabinet. 



4. A portion of the disc of Pt. Crouchii, showing the truncated posterior margin and 



the deep insertion of the spine. 



5. One of the largest specimens (an internal cast) of Pt. rostratus yet found. Here- 



fordshire. M. P. G. 



6. Oyatliaspis Banksii, a very well-preserved and complete shield. Kington. 



Mr. Lightbody. 



7. Disc of Pt. rostratus, with rostrum, cornua, and spine detached. Compare with 



PI. Ill, figs. 3, 8, and 10. Abergavenny. Author's cabinet. 



8. Pt, rostratus, showing, on the left side, the oval perforation of the cornua. 



