68 Bower .—Studies in the Phytogeny of the Filicales . VII. 
source, through types of the nature of Loxsomopsis and Thyrsopteris. They 
culminated in the Davallioid sequence. 
20. The Pterid series are distinguished from the Dicksonioids by the 
lateral fusion of their marginal sori, which are linked together by vascular 
commissures. 
21. They are related to the Dicksonioids as a collateral branch, 
attaching probably in the neighbourhood of Microlepia. They culminated 
in Acrostichum , L. * 
22. The Cheilanthoideae have usually been ranked with the Pterids. 
But until they have been tested by detailed examination, there is not 
sufficient reason to assume a near phyletic relationship. 
23. All the Ferns here treated belong to the Marginales. In the 
methods of their advance they show analogies with the Superficiales, and 
in particular this is seen in those of their forms which have apparently 
superficial sori. These are here shown to result from a slide of the marginal 
sorus to a superficial position. In some cases this is ontogenetic, in others 
phylogenetic as revealed by comparison. 
24. The Superficiales are believed to represent Ferns in which that 
slide took place so early in their descent that the two sequences must be 
held to be phyletically distinct, notwithstanding those analogies. 
