170 OSTEOSTRACI. 
P. 2253, P. 2255. Two specimens, one in the form of a thick 
quadrate plate ; Bush Pitch. Egerton Coll. 
P. 4478. Several fragments; Bush Pitch. Enniskillen Coll. 
P. 5087. Coarse fragment; Bush Pitch. 
Presented by John Edward Lee , Esq., 1885. 
Order II. OSTEOSTEACI. 
Exoskeleton consisting of calcifications, partly with bone-cor¬ 
puscles ; each plate comprising three superposed layers, the middle- 
layer solid, with a coarse reticulation of large vascular canals. 
Dermal sense-organs leaving no impressions upon the exoskeleton. 
Dorsal shield consisting of one principal piece, sometimes with a 
separate mesial piece or fused body-scales posteriorly ; orbits close 
together. Ventral shield simple, or replaced by polygonal calcifica¬ 
tions. [Jaws never preserved.] Paired fins absent. 
Synopsis of Families. 
Surface of shield tuberculated ; interorbital 
piece fixed. Cephalaspidje (p. 176). 
Surface of shield finely punctate; interorbital 
piece loose . Trematasphue (p. 201). 
'A 
uvf* ** - y Jo A „ ‘A T 
A ijc ■ Z 3 ' 
/i />— FamiIy CEPHALA SPIDiE. 
,j ;J \ rf v^aMroi^d^-pr tapering in front, abruptly truncated behind ; 
' *." 1 *7 inteyorbltal piece firmly fixed ; ornamentation consisting of more or 
' ' : iess numerous tuberculations. [The middle layer of the shield 
/ q tTA ' o sometimes produced postero-laterally into a pair of flexible expan- 
J. " sums (? opercula).) Dorso-lateral squamation consisting of series 
t ^oTveiy d^|p and narrow, imbricating scales. 
r I d^> - o Synopsis of Genera. 
^ I. Anterior dorsal body-scales not fused into a con- 
tinuous plate. 
9 Postero-lateral angles of shield produced into 
, \ 1 ' aL acute cornua not exceeding the shield in 
dC V - $ ( ^ #e "R th . Cephalaspi,s (p. 177). 
\ 
