CHAEACTEES OF TEIBES AND GENEEA. 343 



as a distinct natural order of Ferns, which I do not deem 

 it desirable to adopt. I must, however, admit that it has 

 no direct affinity with any other family of Ferns, except 

 with the tribe Saccolomoce, through the genera Loxsoma 

 and Microlepia. 



The peculiarity of the sporangia consists in being ses- 

 silely attached by its inner side to the columnar receptacle, 

 the point of attachment being central, or more generally 

 eccentric towards the lower limb, and the numerous spo- 

 rangia being compactly seated round the receptacle, they 

 consequently acquire a flattened form, each having an arti- 

 culated ring passing round it, at a more or less oblique or 

 at a right angle with the point of attachment, being thus 

 analogous to the flattened sporangia of many Cyathece, as 

 noticed at page 41. 



Most authors place the whole of the species under the 

 genera Hymenophyllum and Trichomanes. On comparing 

 the respective characters of these two genera it will be 

 observed that their technical distinctions are not very 

 definite, depending chiefly upon the difference in length 

 and more or less bilabiate character of the indusium, in 

 conjunction with the varying length of the sporangiferous 

 receptacle. In those species which may respectively be 

 considered as typical, these characters are sufficiently mani- 

 fest, and leave no doubt as to the genus to which they 

 should be referred ; but the numerous intermediate forms, 

 and the different appearances presented by some species at 

 different periods of growth, often render the determination 

 of the genus by herbarium specimens very embarassing, 

 and the difficulty is still further increased by the fact that 

 the two genera contain individual species agreeing perfectly 

 in general habit. It therefore appears to me that the 

 distinction between Hymenophyllum and Trichomanes is 



