ON SOME ARMOURED FISHES. 
11 
Ostracion (PL II., Fig. 3, Ostracism bicaudalis , West Indies), 
drawn for comparison from a specimen in the British Museum. 
From the structure and form of these head-shields, and the 
different position of the eyes in some of them, Professor 
Lankester has divided the genus Cephalaspis into three sub- 
generic types, namely: — Eucephalaspis (Woodcut, Fig. 7), 
Hemicyclaspis (Woodcut, Fig. 8), and Zendspis. 
Fig. 8. 
outline of head shield of Hemicyclaspis Murchisoni, EGERTON 
(after Lankester). 
Eucephalaspis includes the celebrated specimen named by 
Agassiz after Sir Charles Lyell, in which the form of the body 
is very well preserved (see restoration, Plate I., Fig. 4). 
Other species (E. Powriei and E. Pagei ) have been added by 
Lankester ; also showing the general form of the body, with the 
pectoral, dorsal and caudal fins ; and the actual scales, which, in 
E, Lyelli , are not preserved. Hemicyclaspis Murchisoni best 
shows that very peculiar polygonal division of the surface of the 
carapace (Woodcut, Fig. 6), which Professor Huxley has called 
attention to ( ante p. 10). This peculiar ornamentation is not 
always present, other head-shields being ornamented by tubercles 
of various forms and sizes. (See Woodcuts, Figs, 7 a, 9, and 10a.) 
The largest of these buckler-headed fishes belongs to the 
genus Zenaspis , a head-shield having been obtained by Mr. 
John Edward Lee, F.G.S., from the 44 Cornstones 55 (Lower Old 
Red Sandstone) of Herefordshire, measuring 7 inches by 7 
inches. 
A characteristic example of Cephalaspis , discovered by Prin- 
cipal Dawson, of Montreal, in the Devonian sandstones of Gaspe 
