AND BUXBAUMIA. 343 



Hymenostomum or Leptostomum. A membrane of this kind 

 is certainly present in some species of Gymnostomum, and 

 perhaps may be found in all those that really belong to 

 that genus. It exists also in Weissia Templetoni, which so 

 closely resembles Gymnostomum fasciculare as to be with 

 difficulty distinguished from it, unless by the inspection of 

 the peristomium; and, in addition to the erect annular 

 peristomium from which the character of the genus is 

 taken, I have observed a similar membrane in Leptostomum 

 itself. It seems even to be not an uncommon process or 

 termination of the inner membrane, though it has been 

 remarked only in some of its more obvious and persistent 

 modifications. Thus the spongy membrane figured and 

 described in the two published species of Calymperes, seems 

 to be an analogous structure,-' as is also the circular disk 

 termiuating the columella in several species oiSplachnum; w* 

 and perhaps even the tympanum of Polytrichum may be of 

 similar origin. 



But these characters of Leptostomum and Hymenostomum, 

 though they do not appear to have been yet observed in 

 any other mosses, may still perhaps be considered too 

 minute for generic distinctions : and it must be admitted 

 that were nothing to be obtained but the subdivision of an 

 extensive natural genus it could not be necessary to have 

 recourse to them. The divisions in question, however, are 

 certainly not of that kind. 



The weakest part indeed of Hedwig's system is its 

 bringing together all those mosses that have a naked peri- 

 stomium, and even including the greater part of them in 

 the genus Gymnostomum ; while many of the species so 

 associated are in real affinity much nearer to several other 

 genera of the order having a simple or even a double 

 peristomium. 



' The circular spongy membrane covering the mouth of the capsule certainly 

 does not form an essential part of the character of Galym.'peres ; for, in the only 

 species that I have examined, it is either entirely wanting, or firmly adheres to 

 the inner surface of the operculum, along with which, also, a considerable por- 

 tion of the columella separates. Nor has Swartz, who established the genus (in 

 Spreng. Schrad. und Link Jahrb. der Oewdch. vol. i, p. 1) even noticed this 

 membrane in his description. 



