296 THE OLDEST AIR-BREATHERS 



Scorpions are referred by Scudder to three species belonging 

 to two genera. 1 



In the previous paper we have considered the mode of 

 accumulation of Coal, and it may be useful here to note the 

 light thrown on this subject by the Air-breathers of the coal 

 formation and their mode of occurrence. 



In no part of the world are the coal measures better 

 developed, or more fully exposed, than in the coast sections of 

 Nova Scotia and Cape Breton ; and in these, throughout their 

 whole thickness, no indication has been found of any of the 

 marine fossils of the Lower Carboniferous Limestone. Abun- 

 dant remains of fishes occur, but these may have frequented 

 estuaries, streams and ponds, and the greater part of them are 

 small ganoids which, like the modern Lepidosteus and Amia, 

 may have been specially fitted by their semi -reptilian respira- 

 tion, for the impure waters of swampy districts. Bivalve 

 mollusks also abound ; but these are all of the kinds to which 

 I have given the generic name Naiadites, and Mr. Salter those 

 of Anthracomya and Anthracoptera. These shells are all 

 distinct from any known in the marine limestones. Their thin 

 edentulous valves, their structure consisting of a wrinkled 

 epidermis, a thin layer of prismatic shell and an inner layer of 

 imperfectly pearly shell, all remind us of the Anodons and 

 Unios. A slight notch in front concurs with their mode of 

 occurrence in rendering it probable that, like mussels in 

 modern estuaries, they attached themselves to floating or 

 sunken timber. They are thus removed, both in structure and 

 habit, from truly marine species ; and may have been fresh- 

 water or brackish-water mussels closely allied to modern 

 Unios. 



The crustaceans {Eurypterus^ Diplostylus^ Cyprids)^ and the 



* Mazonia Acadica, and a second species of Mazonia, with fragments 

 of a third species, generally distinct. Proceedings Royal Society of London, 

 1892. 



