FISHES OF THE DEVONIAN AGE. 43 
essential characters of the sturgeons. The number and size of the body- 
scutes of the sturgeons vary much. In Scaphirhynchus they are nearly con- 
tiguous; in Polyodon they are absent; and of the sturgeons with few or no 
scutes nothing but the cranium would be likely to be preserved in fossiliza- 
tion. Ihave often found on the beaches of islands in Lake Erie the remains 
of sturgeons thrown up by the waves. These usually consist of scattered 
dermal scutes and the brain-box; often the cranium alone was found, a 
hollow shell of bone, from which all the appendages of the under side and 
interior had been removed by decay. ‘The resemblance of such an object 
to the cranium of Macropetalichthys is striking, and when we compare the 
cranial plates of both, there seems to be as close correspondence as we often 
find between living and fossil fishes. I give below a diagram of the cranial 
plates of Macropetalichthys with my reading of their homologies. 
I have mentioned in the Palze- 
ontology of Ohio that MMacropeta- 
lichthys occurs in the Devonian lime- 
stone of Germany, and have referred 
to the fact that the cranium of a 
species of this genus was described 
by von Meyer' with the name of 
Placothorax Agassizi, as he supposed 
his fossil to be generically identical 
with Placothoraz of Agassiz; but 
these fossils have really no relation- 
ship with each other. Placothorax 
is nothing but the pectoral organ of 
a large species of Pterichthys. Von 
Meyer’s specimen is also reversed, 
phe 5 Fic. 2. Cranial plates of Macropetalichthys. 
the occipital bone being taken for p.pmmoia. Fr. Frontal. Pa. Parietal? 
8. O. Supra-occipital. O. Orbital. Sq. Squamosal? 
the nasal, ete. By reference to hig Pr. F. Pre-frontal. P.O, Post-orbital. Ep. Epiotic? 
figure’ this will be seen at a glance. Unfortunately the tuberculated 
1 Neues Jahrbuch fiir Mineral., 1846, p. 596. ? Palaeontographica, vol. 1, p. 102, Pl. XII. 
