THE BRYOPHYTA OF ICELAND 619 



In the lollowing pages some examples of Ihe Bryophyte vege- 

 tation of lava-clefts will be described. 



Thingvallahra un. The lava-clefts (Icelandic Gjå) there, are 

 pecLiliar on account of their unusual depth (as much as 20 — 30 

 metres). Several of those situated nearest to the lake of Thingvellir 

 have deep water at the bottom. 



The Bryophyte carpet at the bottom of the clefts is composed 

 of Hylocomiiiin loreiim, H. proliferiini, H. parietiniim, H. squarrosiim, 

 Hypniim iincinatiim, H. callichrouin, H. straminenm, H. niolluscum, 

 Eiirhynchiuin piliferum, Antitrichia ciirtipendula, Polytrichnm alpinuin, 

 Rhacomitriiim hypnoides, R. canescens, Dicranum Blyttii, D. Starckei, 

 D. molle, Sphagnum teres, S. Girgensohnii, Lophozia ventricosa, L. 

 (juinquedeniata, L. Kiinzeana, L. alpestris, Ptilidium ciliare and Sca- 

 pania irrigiui. On the sides of the clefts there grew especially An- 

 (vctangiiim compactiim, Grimmia torquata, G. funalis, Gymnostomum 

 riipestre, Amphidiiim Moiigeottii and A. lapponiciim. Intermixed with 

 these, and in cushions on the ledges, in the crevices and among 

 the blocks there grew: Hypnum cupressiforme, Isothecium teniiinerve, 

 Plagiothecium pulchellum, P. denticulatum, P. sihaticum, Amhlystegium 

 Sprucei, Neckera complanata, Schistidium gracile, Rhacomitrium siide- 

 ticum, Sælania cæsia, Ditrichum flexicaule, Tortella tortiiosa, Fissidens 

 osmiindoides, F. bryoides (rare), Pohlia cruda, P. commutata. Bartramia 

 ityphylla, Conostomnm horeale, Philonotis tomentella, Mnium orthor- 

 rhynchum, Hryum pallens, Plagiobryum Zierii, Distichiiim montanuni, 

 Diplophyllnm albicans (in abundance), Lophozia heterocolpos, Lejeunea 

 cavifolia, Blepharostoma trichophyllnm, Aliciilaria scalaris, A. geo- 

 scypha, Anthelia Jnratzkana, Scapania subalpina, Pleuroclada albescens 

 var. islandica, Cephalozia bicuspidata, Eucalyx snbellipticus, Gymno- 

 mitrium concinnatnm, Metzgeria fnrcata, Radnla complanata, Aneura 

 pinguis and Preissia commntata. 



The above list is very long, but is nevertheless hardly complete, 

 since some of the common chomophytes are not enumerated in it, 

 and, at any rate, several of them were undoubtedly forgotten, while 

 the list was being made on the spot, but it gives a good idea of 

 the exceedingly great number of species which are found in these 

 localities. 



Hafnarfjardarhraun. Aimost the same species are found 

 there as in Thingvaliahraun, but the situation close to the sea-side 

 makes its influence felt. Rhacomitrium heterostichum and R. fasci- 

 culare are exceedingly common, and in several piaces Ulota maritima 



40* 



