OSTEOSTRACI. 



11 



Ledbury, Herefordshire. The typical species C. lyelli, with well-developed 

 cornua, is characteristic of the Lower Old Red Sandstone of Forfarshire. 

 Other species are known from corresponding horizons in Caithness, Ayr- 

 shire, and New Brunswick; while one specimen is recorded from the 

 Upper Devonian of Scaumenac Bay, P. Q., Canada. The largest known 

 head-shield (Cephalaspis magnified, from the Caithness flagstones) measures 

 0-22 m. in length. 



FIG. 10. 



Cephalaspis murchisoni ; restoration, lateral aspect, about one-half nat. size. 

 U. Silurian and L. Old Bed Sandstone Passage Beds ; Herefordshire. 

 (From Brit. Mus. Catal.) 



Auchenaspis (or Thyestes) comprises only small species, 

 differing from Cephalaspis in their depressed form and in the 

 fusion of some of the anterior body-scales with the head-shield. 

 A. salteri occurs in the Ludlow Tile-stones, A. egertoni (fig. 11) 



FIG. 11. 



Auchenaspis egertoni; head and trunk, upper aspect, nat. size. L. Old Bed 

 Sandstone Passage Beds; Herefordshire, orb. , orbits ; p.o.v. , postorbital 

 depression. 



in the Lower Old Red Sandstone Passage Beds of Ledbury, and 

 A. verrucosa in the Upper Silurian of the Isle of Oesel, Baltic 

 Sea. Eukeraspis is a name given to small shields from the 

 Upper Ludlow and Downton Sandstone of Herefordshire, 

 characterized by much-produced slender cornua. 



The Tremataspidae, of which only the shield is certainly 



