302 THE OLDEST AIR-BREATHERS 



Nova Scotia it would seem that a few snails, gally-worms, and 

 insects were the sole links of connection between the plant 

 creation and air-breathing vertebrates. Is this due to the 

 paucity of the fauna, or the imperfection of the record ? The 

 fact that a few erect stumps have revealed nearly all the air- ' 

 breathers yet found, argues strongly for the latter cause ; but 

 there are some facts bearing on the other side. 



A gally-worm, if, like its modern relatives, hiding in crevices 

 of wood in forests, was one of the least likely animals to be 

 found in aqueous deposits. The erect trees gave it its almost 

 sole chance of preservation. Pupa vetusta is a small species, 

 and its shell very thin and fragile, while it probably lived among 

 thick vegetation. Further, the measures 2,000 feet thick, 

 separating the lowest and highest beds in which it occurs, in- 

 clude twenty-one coal seams, having an aggregate thickness of 

 about twenty feet, three beds of bituminous limestone of animal 

 origin, and perhaps twenty beds holding Stigmaria in situ, or 

 erect Sigillarice and Calamites. The lapse of time implied by 

 this succession of beds, many of them necessarily of very slow 

 deposition, must be very great, though it would be mere guess 

 work to attempt to resolve it into years. Yet long though this 

 interval must have been, Pupa vetusta lasted without one iota 

 of change through it all ; and, more remarkable still, was not 

 accompanied by more than two other species of its family. 

 Where so many specimens occur, and in situations so diverse, 

 without any additional species, the inference is strong that no 

 other of similar habits existed. If in any of those subtropical 

 islands, whose climate and productions somewhat resemble 

 those of the coal period, after searching in and about decaying 

 trees, and also on the bars upon which rivers and lakes drifted 

 their burdens of shells, we should find only three species, but 

 one of these in very great numbers, we would surely conclude 

 that other species, if present, were very rare. 



Again, footprints referable to Dendrerpeton, or similar animals, 



