FOSSILS OF THE LIAS. 
359 
Fig. 3TT. 
Acrodm nobilis, Agass. (tooth); commonly called “fossil leech.” 
Lias, Lyme Regis, and Germany. 
But the remains of fish which have excited more attention 
than any others are those large bony spines called icMhyo- 
doruUtes (a. Fig. 378), which were once supposed by some 
Fig. 3T8. 
a h 
Hyhodus reticulatiis, Agass. Lias, Lyme Regis. 
a. Part of fin, commonly called Ichthyodorulite. b. Tooth. 
naturalists to be jaws, and by others weapons, resembling 
those of the living Balistes and Silurus; but which M. 
Agassiz has shown to be neither the one nor the other. The 
spines, in the genera last mentioned, articulate with the 
backbone, whereas there are no signs of any such articula¬ 
tion in the ichthyodorulites. These last appear to have been 
bony spines which formed the anterior part of the dorsal fin, 
like that of the living genera Cestracioii and Chimcera (see 
a, Fig. 379). In both 
of these genera, the 
posterior concave face 
is armed with small 
spines, as in that of the 
fo s s i 1 Hybodits (Fig. 
378), a piacoid fish of 
the shark family found 
fossil at Lyme Regis. 
Such spines are simply 
imbedded in the flesh, CMmcera monstrosa* 
and attached to strong 
muscles. “ They serve,” says Dr. Buckland, “ as in the Chi¬ 
mcera (Fig. 379), to raise and depress the fin, their action 
* Agassiz, Poissons Fossiles, vol. iii., tab, C, Fig. 1. 
