THE CARBONIFEROUS AGE. 157 



ladder-tracks and pitted tracks* of the Silurian and 

 Primordial, but that with the strokes of their rounded 

 or spinous tails, the digging of their snouts, and the 

 hoe-work of their hard upper lips, or Hypostomes, 

 they made nearly all those strange marks in the Pri- 

 mordial mud which have been referred to fucoids, and 

 even to higher plants. The Trilobites worked over 

 all the mud bottoms of the Primordial, even in places 

 ^here no remains of them occur, and the peculiarities 

 of the markings which they left are to be explained 

 only by a consideration of the structures of individual 

 species. 



I had almost lost sight of the fishes of the Carboni- 

 ferous period, but after saying so much of those of 

 the Devonian, it would be unfair to leave their suc- 

 cessors altogether unnoticed. In the Carboniferous 

 we lose those broad-snouted plate-covered species 

 that form so conspicuous a feature in the Devonian; 

 and whatever its meaning, it is surely no accident 

 that these mud-burrowing fishes should decay along 

 with those crustacean mud-burrovvers, the Trilobites. 

 But swarms of fishes remain, confined, as in the De- 

 vonian, wholly to the two orders of the Gar-fishes 

 (Ganoids) and the sharks (Placoids). In the former 

 we have a multitude of small and beautiful species 

 haunting the creeks and ponds of the coal swamps, 

 and leaving vast quantities of their remains in the 

 shaly and even coaly beds formed in such places. 

 Such were the pretty, graceful fishes of the genera 

 * Cliinactichnittm and Protichnitcs. 



