﻿1 60 HETEROSTRACI. 



Synopsis of Genera. 



I. Orbits enclosed in dorsal shield. 



Shield consisting of seven parts, fused in adult. Pteraspis (p. 160). 



II. Orbits forming lateral notches in dorsal shield. 



Shield consisting of a single plate Palcsaspis (p. 169). 



Shield consisting of four parts , Cyathaspis (p. 170). 



Genus PTERASPIS, Kner & Huxley. 



[R. Kner, Haidinger's Naturw. Abhandlungen, vol. i. 1847, p. 165 ; 

 emend. T. H. Huxley, Quart. Journ. Geol. Soc. vol. xvii. 1861, 

 p. 166.] 



Syn. Palceoteuthis, F. Roerner, Palaeontogr. vol. iv. 1855, p. 72. 



Archceoteuthis, F. Roemer, in Bronn's Leth. Geognostica, vol. i. 



1855, p. 520. 

 Scaphaspis, E. R. Lankester, Rep. Brit. Assoc. 1864 (1865), Trans. 



Sect. p. 58 (in part). 



Dorsal shield arrow-head-shaped, consisting of seven separately 

 calcined portions : — a large central disc, with a triangular azygous 

 rostral jplate anteriorly and a large median dorsal spine posteriorly ; 



Fig. 14. 



Pteraspis rostrata (Ag.). — Dorsal shield restored, after Lankester. 



a pair of orbital plates, completely enclosing the orbit on either side 

 and partially inserted between the rostrum and central disc ; and a 



