AIR-BREATHERS OP THE COAL PERIOD. 277 



mass a quantity of thick crust or shell occurs, which under the 

 microscope presents a minutely tubular and laminated appear- 

 ance, resembling that of the shell of a crustacean rather than 

 any other kind of structure with which I am acquainted. There 

 may have been laud-crabs in the coal period; but it is perhaps 

 more likely that some one of the larger individuals of Dendrer- 

 jaeton had been feeding on crustaceans in some pond or creek, 

 before it fell into the pit in which it was entombed. It is how- 

 ever interesting to observe that no remains whatever of fishes 

 have occurred in any of this coprolite or in the erect trees contain- 

 ing reptile bones, though such remains are very abundant in some 

 of the associated beds. This fact confirms the inference dedu- 

 cible from other considerations, that the ground in which these 

 open pits presented themselves, was not that of a very low swamp, 

 liable to inundation, or very near to the sea or other bodies of 

 water. 



I may notice here certain very remarkable impressions, the 

 origin of which I am at a loss to conjecture, but which may have 

 had some relation to reptiles of the coal period. They occurred 

 on the surface of a layer of grey sandstone about 60 feet above 

 the bed containing the erect reptiliferous trees. This bed is one 

 of a series of flaggy layers on which occur, with vegetable frag- 

 ments, tracks, possibly of Hylonomus, and rain-marks. The im- 

 pressions now referred to were thus described by me in 1861 : 



M They consist of rows of tranverse depressions, about an inch 

 in length and one-fourth of an inch in breadth. Each trail con- 

 sists of two of these rows running parallel to each other, and 

 about six incbes apart. Their direction curves abruptly, and they 

 sometimes cross each other. From their position they were pro- 

 bably produced by a land or fresh-water animal — possibly a large 

 Crustacean or gigantic Annelide or Myriapod. In size and gene- 

 ral appearance they slightly resemble the curious Climactichnites 

 of Sir W. E. Logan, from the Potsdam sandstone of Canada." 

 To this I have only to add that the space between the rows of 

 of marks is slightly depressed and smoothed, as if with a heavy 

 body, like that of a serpent, trailed along. 



I have given in Fig. 54, as a supplement to the history of Den- 

 drerpeton and Hylonomus, a diagram of the form of the skull and 

 the character of the dentition, restored from actual specimens 

 This will serve further to illustrate the descriptions in previous 

 sections. 



