THE CARBONIFEROUS SYSTEM 291 



i 



Plants of the Middle Stage 



In this stage Sigillaria is more abundant than Lepidodendron, 

 S. elongata, S. polyploca, and S. Brardii being common species. 

 Calamites and Sphenophyllum are also very abundant, though no 

 species is restricted to this division. Fern-like fronds abound, 

 Sphenopteris and Neuropteris reaching their maximum development. 

 Of the former S. (Ztillaria) delicatula, S. (Corynepteres) coralloides 

 are characteristic species. 



Plants of the Transition Stage 



These are a mixture of typical middle stage forms, such as 

 Pecopteris Miltoni, Anmilaria radiata, Sphenophyllum cuneifolium, 

 and Alethopteris lonchitica, with species characteristic of the Upper 

 stage, such as Alethopteris Serli, Neuropteris rarinervis, and Spheno- 

 phyllum emarginatum. 



Plants of the Upper Stage 



In these beds Calamites become rare, Lepidodendron is not 

 common, and Sigillaria also less abundant. The most abundant 

 plants are fronds of the Pecopteris form, such as P. arborescens, 

 P. oreopteridea, P. polymorpha, and P. cyathea, but some forms of 

 Neuropteris (N. rarinervis, N. macrophylla, and N. o-vata are 

 common. Alethopteris Serli and Cordaites angulosostriatus are also 

 typical Upper Coal-measure species. 



2. The Land and Freshwater Fauna 



a. Mollusca. In the Coal-measure shales, and associated with 

 many of the plants above mentioned, shells somewhat resembling 

 the recent Unio are frequently found. They have been referred 

 chiefly to three genera, Carbonicola ( = Anthracosia"), Anthracomya, 

 and Naiadites, and their affinities have recently been studied by 

 ] )i . W. Hind, who refers the first two genera to the Unionidce and 

 the third to the Mytilidce, but believes that all of them were fresh- 

 water forms. He remarks that their occasional or rare association 

 with marine shells is no proof that they were capable of living in 

 salt water, for their shells may have been carried down by rivers 

 into bays and estuaries. 



b. Arthropods. True Insects, Myriapods and Arachnids, have 

 also been found in the Coal-measures, including crickets, beetles, 

 .and a scorpion. Crustacea also inhabited the waters, the small 

 Ostracoda Bairdia, Leperditia, and Beyrichia, and the Phyllopod 



