May, 1906.] Key to Liverworts. 537 



2. Midrib covered above and below with 2 rows of enlarged cells; 



hairs very long, divaricate and hooked-deflexed, the marginal 

 in twos, rarely with disccid tips. hamata Lindb. 



Midrib covered above with 2 rows of enlarged cells and below 

 with 3-7 rows of cells. 3. 



3. With 3-7 (usually 4-6) rows of cells below, smaller than the upper 



ones and often indistinct; midrib densely pilcse beneath, hairs 

 rather long, straight cr nodding, the marginal mcstly in clus- 

 ters of 3-6, some of which have disccidal tips. 



myriopoda Lindb. 

 With 3-6 rows of enlarged cells below; hairs rather long, straight, 

 divaricate, the marginal usually in twos, very often disk- 

 bearing. " ' conjugata Lindb. 

 Mylia S. F. Gray. 



Stem erect, nearly simple, radiculose; leaves orbicular, purplish; 

 perianth oval; calyptra finally long-exserted. 



Taylori S. F. Gray. 

 Nardia S. F. Gray. 



1. Perianth exserted , connate with the involucral leaves, subcampan- 



ulate and open, deeply laciniate, 6-10 plicate; rootlets purple. 



fossombroyiioides, Lindb. 

 Perianth connate at base with the inner involucral leaves and some- 

 what surpassing them, 3-8 carinate, the mouth constricted; 

 rootlets whitish reddish or purple. 2. 



2. Marginal leaf-cells quadrate and much larger than the others; 



rootlets whitish. crcnitlata Lindb. 



Marginal leaf-ecUs about as large as the others. 3. 



3. Branch leaves ovate or obovate, scarcely decurrent, half as large 



as the obliquely semi-circular cr brcadly ovate, decurrent 

 stem leaves; fruit unknown. biformis Lindb. 



Branch leaves similar to the stem leaves; fruit known. 4. 



4. Rootlets reddish (claret-colored); leaves roundish oval; involucral 



leaves clcsely appressed and connate with the lower third of 

 the perianth, which is slightly exserted, obovate and narrowed 

 to the 4-cleft mouth. ' ' hyalina Carring. 



Rootlets purple; leaves orbicular; involucral leaves connate (more 



or less) with the small, subobovate perianth, which is slightly 



or not exserted, rooting at base and triquetrous above, but 



beccming 4-7 plicate. crcnuliformis Lindb. 



Notothylas Sulliv. 



Thallus 5-15 mm. wide; capsule with a suture on each side; spores 

 light yellowish-brown. orbicularis Sulliv. 



Thallus small; capsule often without suture; spores dark-brown, 

 a half larger. mclanospora Sulliv. 



Odontoschisma Dumort. 



Underleaves inostly wanting; perianth subulate-fusiform, lacinate 

 or cliiate; among mosses. Sphagni Dumort. 



LTnderleaves broadly oval, entire and sub-denticulate; perianth 

 close-connivent above at length bursting irregularly; on rotten 

 wood. doiitdata Lindb. 



Pallavicinia S. F. Gray. 



Fruit arising from the costa, at first terminal, becoming dorsal; 

 capsule cylindric, about 5 times longer than broad; involucre 

 cup-shaped, short-lacerate. LycUii S. F. Gray. 



Pellia Raddi. 



1. Thallus indistinctly costate, lobed and sinuate. Calyptra much 

 longer than the involucre. Antheridia at the base of the in- 

 volucre on the same thallus. cpiphylla Raddi. 



