ISOTHECII. 139 



ing about halfway ; paraphylla thread-shaped, simple, or 

 branched; fruitstalk about an inch long; sporangium oval, 

 oblong, suberect or cernuous ; cilia of inner peristome delicate, 

 but not abortive; lid rostrate. 



The rostrate beak, shorter nerve, and more ovate leaves 

 distinguish this from P. atrovirens. 



ORDER VI. ISOTHECII, Br. & Sch. (Leucodonteis inclusis) 



Stems with the imbricated leaves cylindrical; leaf-cells 

 narrow and rhomboid, or small and suborbicular ; sporangia 

 erect, symmetrical; peristome single or double; inner peri- 

 stome when present without intermediate cilia ; calyptra hood- 

 shaped. 



1. Leaf-cells ivith their walls hexagonal, rhomboid, or linear, some- 

 times quadrate at the angles of the leaves. 



13. ISOTHECIUM, Brid. 



Sporangium erect, cylindrical; ring deciduous; peristome 

 double; inner membrane divided halfway down into 16 keeled 

 perforate processes, with obscure intermediate cilia ; cells of 

 the leaves narrow, elongated ; primary stem creeping, secon- 

 dary dendroid. 



1. I. myurum, Brid.; secondary stem with fasciculate 

 incurved branches; leaves ovato-oblong, shortly acuminate, 

 toothed at the apex ; nerve reaching halfway up ; perichsetial 

 leaves erect ; sporangium ovate, narrow ; lid conical, rostrate. 

 Hook. $ Wils. t. xxv.; Eng. Bot. t. 1566.; (Mouy. $ Nest, 

 n. 331.) 



On walls and trees. Bearing fruit in early spring. 



Dioicous ; forming soft wide pale tufts. Primary stem 

 creeping, throwing out secondary, erect, slightly procumbent 

 stems, which are divided above in a dendroid manner ; branches 



