Mr. Brown on LyelUa, Leptostomnm, and Btixbaumia. 581 



bly, in some degree, prevent dispersion, while the unequal di- 

 stances of the teeth might either produce a deviation from the 

 regular figure, or an early rupture, of the tympanum, which forms 

 an essential part in this economy. 



BUXBAUMIA. 



In my former paper I have proposed to preserve the genus 

 Btabaumia, as established by Schmidel; and in constructing a 

 character to comprehend both species, I entirely rejected the 

 outer peristomium of Hedwig; and having also adopted his opi- 

 nion respecting the middle peristomium of B. aphylla, which he 

 has termed corona, and considered as analogous to the annulus in 

 many other mosses, it became unnecessary to advert to this part 

 in defining the genus. 



Mr. Hooker has since published an excellent analysis of both 

 species, and has followed Ehrhart and Mohr in regarding them 

 as forming distinct genera. 



This determination I have now no hesitation in adopting ; for, 

 whatever the nature of Hedwig's corona may be, it affords at 

 least an obvious character, and is connected with other differences 

 of sufficient importance to justify the separation ; though the two 

 genera must always remain in the same natural section of the 

 order. 



The observations that follow belong, therefore, solely to Bux- 

 haumia aphylla. 



My first remark on this plant relates to its peristomium, on the 

 nature of which, as compared with that of other mosses, at least 

 two different opinions may be formed. 



According to one of these, the outer peristomium of Hooker 

 may with Hedwig be considered analogous to the fimbria or an- 

 nulus existing in many other mosses; and the principal objection 



4 p 2 to 



