PTERIDOPHYTA. 



1513 



in the Devonian and Carboniferous of North America and Europe, 

 are regarded by Sir J. W. Dawson as macrospores or sporocarps of 

 Rhizocarps, under the name of Protosalvinia. Better known is the 

 genus Sphenophyllum (fig. 1377), likewise 

 occurring on both sides of the Atlantic, 

 and ranging from the Ordovician to the Car- 

 boniferous, which many authorities now agree 

 in provisionally placing in this order, although 

 others would refer it to the Equisetaceae. 

 They were small plants with wedge-shaped 

 leaves arranged in regular whorls, after the 

 manner of the existing Marsilia. Another 

 type which is regarded by Dr Feistmantel as 

 closely allied to the preceding is Trizygia, 

 known by a single species from the Lower 

 Gondwanas of India. These plants (if com- 

 plete) are comparatively small, with a slender 

 stem bearing incomplete whorls of wedge- 

 shaped leaves ; each whorl occupying only three sides of the stem, 

 and consisting of six leaves arranged in three dissimilar pairs. They 

 were probably aquatic. 



Here also, according to Sir J. W. Dawson, should be placed the 

 genus Ptilophyton (fig. 1378), which appears to be most nearly 



Fig. 1377. — Leaf of Sphen- 

 ophyllum antiquum ; from 

 the Devonian of Canada. 

 Enlarged and natural size. 

 (After Dawson ) 



Fig. 1378. — Ptilophyton plumosum ; from the Lower Carboniferous of Nova Scotia. 

 The right-hand figure shows a portion magnified. (After Dawson.) 



allied to the Rhizocarps. The genus ranges in North America from 

 the Middle Devonian to the Lower Carboniferous, and is also found 

 in the Old Red Sandstone of Scotland. These organisms, which 

 have been referred to the Algae and Lycopodiacese, are composed 

 of feather-like leaves, apparently bearing macrospores on parts of 

 the stem or petioles. They are considered to have been of aquatic 



