bJD  bD 
AN  EXTINCT  GENES  OE  THE  STUEIONIDiE. 
885 
functions  assigned  to  them  in  this  ancient  ocean,  although  probably  of  the  same  natuje 
as  those  performed  now  by  the  surviving  representatives  of  the  family. 
Explais'ation  op  the  Plates. 
PLATE  LXVII. 
Chondrosteus  acipenseroides,  Agassiz  : — reduced  one-fourth. 
PLATE  LXVIII. 
. 1.  Head  and  pectoral  fins  of  Chondrosteus  crassior^  Egeeton: — reduced  one-third. 
. 2.  Outline  of  the  head  of  Plate  LXVII. 
PLATE  LXIX. 
Anterior  portion  of  Chondrosteus  acipenseroides,  Agassiz  : — reduced  one-fourth. 
PLATE  LXX. 
Anal  and  caudal  fin  of  Chondrosteus  crassior^  Egeeton  : — natural  size. 
Notation  of  Paets. 
P.  Pectoral  fins. 
V.  Ventral  fins. 
D.  Dorsal  fin. 
A.  Anal  fin. 
C.  Caudal  fin. 
5.  Basisphenoid. 
36.  Subopercular. 
e.  Alisphenoid. 
■v.  Interopercular. 
Parietal. 
40.  Ceratohyal. 
8.  Mastoid. 
42.  Glossohyal. 
3.  Presphenoid. 
44.  Branchiostegal. 
11.  Frontal. 
30.  Suprascapular. 
12.  Postfrontal. 
51,  52.  Scapulocoracoid. 
20.  Palatine. 
57.  Metacarpal. 
21.  Maxillaiy. 
69.  Metatarsal. 
22.  Premaxillary. 
n.  a.  Neurapophysis. 
28  a.  Epitympanic. 
n.  s.  Neural  spine. 
28  (Z.  Llypotympanic. 
i.  n.  Interneural  spine. 
»2.  Dentary. 
i.  h.  Interheemal  spine, 
35.  Opercular. 
