258 12 



In some species, especially l)elonging to the group of 7). Sprengelii, a spongy 

 protuberance is to be found at the bases of the pinnæ on the underside, which 

 Metïenius has called an aëropliore. In dried specimens the aërophore may be 

 squamiform, tuberculiform, circular or acute. It is generally found only with the 

 larger pinnæ and is often very small. Its importance as specific character seems 

 to me not always equally great; thus D. opposita is found both with and without 

 aërophore. In other species, e. g. D. limbata, its presence and shape is a charac- 

 teristic peculiarity. 



I have found it necessary here to give a review of my experience of the va- 

 lue and stability of the single characters. As the question here is to divide old 

 collective species into smaller species, a minute examination of all the organs of 

 the plants would be needed, if one were to succeed in gaining an idea of the 

 marks which are of essential value for characterizing the single species. The 

 characters mentioned above have certainly all been used by modern pteridologists 

 as Christ, Hieronymus and Rosenstock, but a test of their value has not been 

 attempted. On the other hand descriptions given by other authors (Baker, Fée) 

 are, as a rule, made so briefly and do not at all mention many essential charac- 

 ters, so that in many cases it will be impossible from them alone to form an idea 

 of the peculiarities of the species described. Even in the descriptions of authors 

 as Jenman and Sodiro, who have given detailed diagnoses of several, partly new 

 species belonging to the group of D. opposita, one will very often look in vain for 

 information on essential marks, thus if the leaf bears hairs both on the veins 

 and on the parenchyma. 



In the following pages I have tried in my descriptions to take into considera- 

 tion ail the characters, arranged in a form, having mainly made use of the excellent 

 diagnoses given by Dr. Rosenstock as a pattern. Besides the descriptions of the 

 new species I have only given more detailed descriptions of such species, the 

 original diagnosis of which does not give a clear idea of the species; under the 

 remaining species I have confined myself to adding some notes as supplements to 

 the original descriptions, especially such as may throw light upon the differences 

 between the species and its relatives. It is, however, a very difficult, or rather 

 impossible thing to characterize such closely allied species in words alone. I have, 

 therefore, found it very necessary to accompany the descriptions by illustrations, 

 which correctly show the habit and other characteristic peculiarities of the species. 

 An illustration of those species which have already been well figured, was of 

 course unnecessary. The parts figured here are a normal pinna with a part of 

 the rachis, most often of an type specimen, natural size, drawn from a kind 

 of nature-print, and two or more segments seen from the underside and twice 

 magnified. In this manner it has been possible to give in a limited space an illu- 

 stration of most of the characters of the species. 



I have now only to add some words on the geographical distribution 

 of the species. Most of the species belonging to the group here dealt with are 



