28 MUSCl-ACROCARPI-PERTSTOMI. [Didymodon. 



From this, Trichostomiim ellipticum may be known by its more crowded 

 spreading acuminated leaves, the glossy rigid more oval capsule, and its 

 much longer and perfectly straight beak to the lid, and deeply divided 

 teeth of the peristome. 



16. Didymodon. Hediv. Didymodon. 



Seta terminal. Peristome single, of 16 or 32 teeth approach- 

 ing in pairs or united at the base. Calyptra dimidiate. (Muse. 

 Brit. t. 2.) — Named from eiidvpog, twin, and o^m, a tooth ; from 

 the approximation of the teeth in pairs, 



1. D. purpureas, Hook, and Taylor, (purple Didymodoii); 

 stems scarcely branched, leaves lanceolate acuminate carinated 

 their margins recurved entire, capsule ovato-cylindraceous 

 oblique substrumose furrowed when dry, lid conical. Muse. Brit, 

 ed. 1. p. 65. ed. 2. p. 113. t. 20. Drum. Muse. Scot. v. 2. n. 49. 

 — Dicranum purpureum, Hedw. Sp. Muse. t. 36. Turn. Muse. 

 Hib. p. 72. Fl. Brit. p. 1217. E. Bot. t. 2262.— D. purpuras- 

 cens, D. Celsii, and D. intermedium, Hedw. — D. strictum, Sm. — 



D. papillosum, Brid. — Trichostomum papillosum, Sm Bryum 



Celsii and Mnium purpureum, Linn, and Bryum papillosum, 

 strictum, tenue and bipartitum of Dicks, may confidently be re- 

 ferred here. 



On the ground and on moist banks, most abundant. Fr. Spring. — 

 Variable as this plant assuredly is in its stems and foliage, it is very 

 constant in the form of the fruit, by which it may always be known. 

 The peristome is that of a Didymodon, but the pairs of teeth are con- 

 nected by transverse bars. 



2. D. inclindtus, Sw. (inclined-fruited Didymodon); stems 

 somewhat elongated, leaves bifarious from a sheathing base 

 subulate, capsule ovate inclined smooth, lid conical. Swartz, 

 Muse. Suec. p. 28. Drum. Muse. Scot. v. 1. n. 53. — Cynontodium 

 inclinatum, Hedw. Sp. Muse. p. 58. — Grimmia inclinata, Fl. Brit, 

 p. 1196. E. Bot. t. 1824. — Swartzia inclinata, Hedw, St. Cr. 

 v. 2. t. 27. — Bryum inclinatum, Dicks. 



Usually on mountain rocks ; but rare. On the sands of Barrie, near 

 Dundee, growing with Weissia nigrita; Mr. Don. Fr. Aug. — The teeth 

 are so broad in this species that were it not for their approximation in 

 pairs, we should certainly rank it with the Weissice. 



3. D. nervosus, Hook, and Taylor, (thick-nerved Didymodon); 

 leaves obovate shortly apiculate their nerve incrassated above, 

 capsule ovate erect, lid shortly rostrate. Muse. Brit. ed. 1. p. 66. 

 ed. 2. p. 115. t. 20. — Grimmia atro-virens, E. Bot. t. 2015. 



On dry banks, especially in maritime situations in the south of 

 England, Wales, and Ireland. Fr. Spring. — This species has wider 

 leaves than its congeners and a nerve remarkably thickened upwards. 

 The 32 teeth approach in pairs, and are, as in D.purpureus, connected 

 by transverse bars. 



4. T).flexifolius, Hook, and Taylor, (wavy -leaved Didymodon); 

 steins more or less elongated, leaves erecto-patent oblongo-ovate 



