CHONDROSXEIDiE. 
25 
the anterior rays of each fin gradually increasing in length to an 
acumination. Pelvic fins remote, the dorsal opposed to this pair; 
caudal fin forked, nearly equilobate. Scales absent, except on the 
upper caudal lobe where they are thick and rhombic, invested with 
ganoine; caudal fulcral scales large, with ganoine. 
Toothing is known of the ossifications in the chondrocranium of 
Chonclrosteus , but many specimens exhibit the chief membrane- 
bones. The parietals (figs. 3, 4, jp.) are longer than broad and 
comparatively small; both these and the large frontals (/.) meeting 
at the middle line in a slightly wavy suture, without any inter¬ 
posed elements or vacuities. The squamosals ( sq .) are larger than 
the parietals, extending as far forwards as the latter; the post- 
frontals (jo.f.) are relatively very small. No cranial bones have 
been recognized in advance of the frontals, and the extent of the 
rostrum is thus undetermined. Cheek-plates are also almost 
wanting, only one suborbital (figs. 3, 5, so.) being observed, bearing 
an upward process ascending towards the postfrontal. A series 
of five supratemporal plates (fig. 4, s.t.), of which the three inner¬ 
most are relatively small, occurs along the occipital border. The 
hyomandibular (figs. 3, 6, Jim.) is shaped as in modern Sturgeons, 
but apparently ossified as far as its lower extremity; and a sym- 
plectic must have been present, although it is doubtful whether 
this was ossified in any part. The pterygo-quadrate arcade exhibits 
only two ossifications on each side, one being a large expanded 
Fig. 3. 
Profile of head of Chonclrosteus cicipenseroides, restored (after Traquair). 
j., jugal. Other letters as in figs. 4, 5. 
element (PI. I. fig. 3, jot.) of pterygoid nature, and the other a 
small V"shaped bone Qo£.) articulated with the maxilla, which 
may be either palatine or eetopterygoid. Sheathing the arcade is 
