26 
ACTINOPTERYGII. 
a long curved maxilla (PL I. figs. 2,3, mx.\ deep behind and much 
contracted anteriorly, meeting its fellow of the opposite side in 
front in a distinct symphysis. Another small membrane-bone, 
abutting upon the postero-superior margin of the maxilla, may be 
regarded as the jugal (PI. I. fig. 3, ju.). The mandible exhibits 
three bones, the dentary being much the largest, the articular and 
angular insignificant. The dentary is somewhat arched, the inferior 
margin being concave; but there is scarcely any tapering at the 
symphysis, and the coronoid region is not elevated. The ossified, 
hour-glass-shaped ceratohyal is frequently shown (PI. I. fig. 2, ch .), 
but nothing further is known of the hyoid apparatus. 
The operculum is relatively small and shaped almost like an 
inverted comma with the tail pointing forwards and upwards 
Pig. 4. 
Cranial roof of Chondrosteus acipenseroides (after Traquair). From specimen 
in Museum of Practical Geology. 
/., frontal; op., operculum ; p., parietal; p.f, post-frontal; p.t., post¬ 
temporal ; s.t., supra-temporal; sq., squamosal. 
(figs. 3, 4, 6, op).). The suboperculum ( s.op >.) is much broader and 
almost quadrate, with produced antero-superior angle. About ten 
branchiostegal rays (hr.) can be counted, the uppermost broad and 
the lowermost narrower; but there are no indications of a gular 
plate. 
The notochord must have been persistent, with no calcifications 
