338 ON LYELLIA, LEPTOSTOMUM, 



been able to detect ; but I observe in many cases an 

 appearance which may perhaps account for the belief in 

 their existence, namely a minute reticulation on the outer 

 surface of the membrane, apparently owing to the cor- 

 responding areolae of the inner surface of the operculum, 

 with which it was originally in contact. 



PolytricJacm is remarkable for the various forms of its 

 capsule. Those species, indeed, in which it is quadrangular 

 have been considered as a distinct genus by Mons. de 

 668] Beauvois. But unless this difference of external form 

 should be found connected with others, either in the habit 

 or in the internal structure, which I believe is not the case, 

 it seems hardly sufficient to justify the subdivision of so 

 natural a genus. 



The symmetrical quadrangular capsule, admitting of a 

 regular cylindrical inner membrane, is a character of inferior 

 importance to the plano-convex or dimidiate capsule, which 

 almost necessarily implies, and in Daiosonia and Lyellia 

 at least is found to be connected with, a corresponding 

 irregularity in the figure of the cavity; and* hence I have 

 introduced this remarkable form into the characters of both 

 these genera. 



On the structure of the inner membrane of the capsule 

 in Tolytriclmm the only observation that I have met with 

 occurs in English Botany, where, in the account of Poly- 

 trichum subrotundum (plate 1624), it is stated that Mr. 

 James D. Sowerbyhas discovered, in this species as well as 

 mPolytricJmm undulaiiim,are&\ membranaceous peristomium 

 within the teeth, which, according to Sir James Smith, 

 " gives quite a new idea of the generic character." 



This inner peristomium, if it may be so termed, which 

 is well represented in the figure referred to, and consists of 

 a horizontal projection of the inner membrane immediately 

 below its apex, will, I believe, be found to exist in all the 

 species of the genus, and in some cases reduces the aperture 

 of the inner capsule to half the size of the outer at the origin 

 of the teeth. It is always, however, quite entire, and, 

 according to my observations, is formed of a doubling of the 



