128 PALAEONTOLOGY 



feeble scales, as if, while its upper parts were shielded with 

 plate-armour, a lighter covering of ring or scale armour 

 sufficed for the less vital parts beneath. In the Asterolepis 

 the arrangement was somewhat similar, save that the plated 

 cuirass was wanting. It was a strongly-helmed warrior in 

 slight scale-armour ; for the disproportion between the strength 

 of the plated head-piece and that of the scaly coat was still 

 greater than in the Pterichthys. The occipital star-covered 

 plates are, in some of the larger specimens, fully three- 

 quarters of an inch in thickness, whereas the thickness of the 

 delicately-fretted scales rarely exceeds a line. 



" Why this disproportion between the strength of the 

 armature in different parts of the same fish should have 

 obtained, as in Pterichthys and Asterolepis, or why, while one 

 portion of the animal was strongly armed, another portion 

 should have been left, as in Coccosteus, wholly exposed, cannot 

 of course be determined by the mere geologist. His rocks 

 present him with but the fact of the disproportion, without 

 accounting for it. But the natural history of existing fish, in 

 which, as in the Pimelodi, there may be detected a similar 

 peculiarity of armature, may perhaps throw some light on 

 the mystery. In Hamilton's Fishes of the Ganges, the habitats 

 of the various Indian species of Pimelodi, whether brackish 

 estuaries, ponds, or rivers, are described, but not their charac- 

 teristic instincts. Of the Silurus, however, a genus of the 

 same great family, I read elsewhere that some of the species, 

 such as the Silurus Glanis, being unwieldy in their motions, 

 do not pursue their prey, which consists of small fishes, but 

 lie concealed among the mud, and seize on the chance 

 stragglers that come in their way. And of the Pimelodus 

 gulio, a little strongly-helmed fish with a naked body, I was 

 informed by Mr. Duff, on the authority of the gentleman who 

 had presented the specimens to the Museum, that it burrowed 

 in the holes of muddy banks, from which it shol ou1 its 



