STRUCTURES OF CHIMAZROIDS 103 
morphosed ; the mandible appears to be azfostylic, or artic- 
ulated directly with the skull cartilage, PQ. The gill 
arches are shark-like, but the hyoid arch appears far less 
modified than in sharks; its upper element, /7JZ, is thus 
unconnected with either the skull or the joint of the jaw; 
its distal element, C//, has, however, developed a series of 
specialized supports for the dermal gill shield, OP. The 
study of the fin supports shows the dorsal elements, 2+ XR, 
representing probably the radial and basal elements to- 
gether, arranged in a single row margined distally by the 
longitudinal ligament, ZZ, supporting the dermal func- 
tional fin, D. The paired fins are readily reduced to the 
plan of those of Fig. 84; their girdles, however, seem to 
have acquired more modified characters, their ventral and 
dorsal elements greatly increasing in size. 
Chimeeroids as a group have received but a small share 
of the attention paid to the other fishes; their living 
forms are few and comparatively rare; their embryology 
and larval history are unknown; and their life habits have 
been suggested only in the work of Dr. Giinther (Cha/- 
lenger Report). His record of the taking of immature 
specimens of Chimera at great depths seems thus far the 
most important clue as to the conditions of their living 
and breeding.* 
Fosstl Chimerotds 
Fossil Chimzeroids have left behind them very imperfect 
records of the history of their group. Like the sharks, 
little more than their dental plates and fin spines have 
usually been preserved. The structures of some of their 
ancient members appear to have differed little from those 
just described in the recent Chimera. In Ischyodus, 
* Cf. also Goode and Bean, on Harriotia, P. U.S. Nat. Mus., XVII. 471-473. 
