Didymodon.] APLOPERISTOMI. 115 



HAB. On mountain rocks, rare. On the sands of Barrie, 

 Scotland, growing with Weissia nigrita. Mr. Drum- 

 mond. 



The teeth of the peristome are so broad as to be remarkable 

 in this genus, and to render it doubtful whether this moss 

 should be arranged where Sir J. E. Smith has placed it, among 

 his Cfrimmits, (the Weissice of Hedwig,) or, as we judge, 

 taking the approximation of the teeth in pairs and the habit of 

 the plant into consideration, whether it should be left where 

 Swartz and Mohr have placed it, under the genus Didymodon. 

 It is an extremely rare species with us, having, since the time 

 of its discovery by Mr. Dickson, been only met with twice ; 

 first by Mr. Mackay on the mountains of Cunnamara in Ire- 

 land, and afterwards by Mr. Drummond in Scotland, in the 

 habitat above mentioned. 



* * Capsules erect, or nearly so. 



3. D. nervosum ; leaves obovate shortly apiculate their nerve 



incrassated above, capsule ovate erect, lid shortly rostrate. 

 (TAB. XX.) 



Didymodon nervosum. Hooker and Tayl Muse. Brit. ed. 1. p. 66. 

 Arn. Disp. Muse. p. 34. 



Grimmia atro-virens. Engl. Sot. 2015. 



HAB. On dry banks, especially in maritime situations, in 



the south of England. 



This species may easily be mistaken for Weissia Zanceolata, 

 and especially for that variety which has been called W. aci- 

 phylla by Mohr ; but the breadth and stronger texture of the 

 leaf, its remarkable nerve, which is thickened above, and its 

 peristome of 32 teeth approached in pairs, are abundantly 

 characteristic marks. This species has wider leaves than those 

 of its congeners. 



4. D. flexifolium ; stems more or less elongated, leaves oblongo- 



ovate flexuose strongly serrated at the point, capsule erect 

 cylindraceous, lid rostrate. (TAB. XX.) 



Didymodon flexifolium. Hooker and Tayl. Muse. Brit. ed. 1. p. 66. 

 Hook. Fl. Scot. P. II. p. 135. Arn. Disp. Muse. p. 35. Hobson, 

 Brit. Mosses, v. 1, n. 50. Drummond, Muse. Scot, v, 2. , 46. 

 H 2 



