150 PALEONTOLOGY. 



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 shot out its 

 armed head, and arrested as they passed, the minute animals 

 on which it preyed. The animal world is full of such com- 

 pensatory defences; there is a half-suit of armour given to 

 shield half the body, and a wise instinct to protect the rest. 

 Now it seems not improbable that the half-armed Coccosteus, 

 a heavy fish, indifferently furnished with fins, may have 

 burrowed, like the recent Silurus Glanis or Pimelodus gidio, 

 in a thick mud, of the existence of which in vast quantity, 

 during the times of the old red sandstone, the dark Caithness 

 flagstones, the foetid breccia of Strathpeffer, and the gray 

 stratified clays of Cromarty, Moray, and Banff unequivocally 

 testify; and that it may have thus not only succeeded in 

 capturing many of its light-winged contemporaries, which it 



