160 
HKTEKOSTRACI. 
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 . Palceaspis (p. 169). 
Shield consisting of four parts... Cyathaspis (p. 170). 
Genus Kner & Huxley. 
[E. Kner, Haidinger’s Haturw. Abhandlungen, vol. i. 1847, p. 165 ; 
emend. T. H. Huxley, Quart. Journ. Geol. Soc. vol. xvii. 1861* 
p. 166.] 
Syn. Palceotenthis, F. Roemer, Paigeontogr. vol. iv. 1855, p. 72. 
Ai cliceoteuthis, 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). ,f*J 
Dorsal shield arrow-head-shaped, consisting of seven separately 
calcified portions :—a large central disc, with a triangular azygous 
rost) al plate anteriorly and a large median dorsal spine posteriorly ; 
Rig. 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 3 
0 — 
