52 
present description is based, which measured 52cm., the 
base of the first dorsal fin ray was only 6mm. from the 
posterior narial aperture of the eyeless side, ~e., well in 
front of the cavity of the brain. 
As in the paired and caudal fins all the fin rays con- 
sist of two pieces. Hach fin ray is connected with two 
further skeletal pieces termed by Cope,* Baur,t and 
Smith Woodwardt the baseost and axonost, by T. J. 
Parker$ pterygiophores, and by Bridgel] radial elements. 
The axonost has hitherto been called the interspinous 
bone, on account of its position between two neural spines. 
The terms baseost and axonost are adopted in this work, 
and the precise connections between these two elements and 
the two pieces forming a fin ray will be described below. In 
the meantime it may be remarked that usually one or two 
axonosts are found between two adjacent neural spines in 
the dorsal and anal fins of the Plaice, whilst the baseost 
is always situated between: and attached to the heads of 
two adjacent axonosts. ‘The two halves of the fin ray 
diverge proximally and tightly clasp the baseost (ep. fig. 
16). This mechanism was first described by T. J. Parker in 
Regalecus, and has since been described in the Plaice by 
Bridge. Each axonost, even in old specimens, consists 
usually of a bony cylinder filled with cartilage. The head 
is always hollow, and is filled up with a triangular plug 
of cartilage (fig. 16). 
The first dorsal fin ray has no baseost, but its halves 
diverge as usual and embrace the head of the first axonost 
with only a small sub-cartilaginous pad between. It is 
also asymmetrical, the ocular half being slightly the 
longer. 
* American Nat., 1890. + Jour. Morph., vol. iii. 
t Catalogue Fossil Fishes, British Museum, and Vertebrate 
Paleontology. 
§ Trans. Zool. Soc., vol. xii. \| Journ. Linnean Soc., vol. xxv. 
