572 Mr. Brown on Lyellia, Lepfostomum, and Buxbaitmia. 



Mr. Hooker, however, has since found, as he states, the same 

 structure in several other mosses, generally considered as having 

 a naked peristomium, particularly in Gymnostomum microstomum, 

 Gr'iffithianum, and fasciculure ; and as these species have but little 

 resemblance to each other, and still less affinity to Leptostomum, 

 he has reduced this genus also to Gymnostomum. 



If the statement referred to be correct, Leptostomum, though it 

 may be a natural genus, must be given up, until other marks 

 shall be found by which it may be distinguished. I have not 

 had specimens sufficiently perfect to enable me to judge, of the 

 structure of all the species of Gymnostomum mentioned by Mr. 

 Hooker. In one of them, however, Gymnostomum microstomum, 

 the peristomiu,m is certainly very different from that of Leptosto- 

 mum. In this species I find, on removing the operculum, that the 

 mouth of the capsule is not only completely covered by a hori- 

 zontal membrane, but that this covering is derived from the outer 

 membrane of the capsule, and consequently differs in origin as 

 well as in form from the peristomium which it has, been said to 

 resemble. Its central portion, however, being extremely thin is 

 soon ruptured and deciduous, and in this state onl}' it has been 

 seen by the authors of the Muscologia Britamiica. 



Gymnostomum microstotmim therefore may itself be considered as 

 a distinct genus, to which the name of Hymenostomum* may be 

 given; and it is worthy of remark, that in its technical character 

 it approaches most nearly to Lyellia, though no two mosses dif- 

 fer more widely in almost every other respect. 



* Hymenostomum. 

 Fl. Fern, terniinalis. 



Stoma edentulum, clausum epipkragmate (e membrana exteriore orto), disco tenuissimo 



(a columella libero) mox rupto et evauido j Umbo pe»sistenti horizoiitali indiviso. 



Calyptra dimidiata, laevis. 



Fl, Mas terminalis, gemmiformis, 



From 



