Uepaticw of North America. 29 



ened beneath, cavernous the entire length; margins thin, undu- 

 late-crisped and crenulate; carina copiously radiculose, tumid 

 from the abundant fruit; capsules single, crowned by a long, 

 obliquely-ascending, funnel-mouthed, exserted style; spores ob- 

 scurely angular, reticulate and margined, submuricate (E. Sul- 

 livanti Aust). 



Hob. Ponds, ditches and wet places; common. (Eu.) The vari- 

 ety in damp ground or cultivated fields. 



Bib. Syn. Hep. p. 6K), Hep. Europ. p. 171. 

 Delin. Lindenberg Monog. Ric. t. XXIV. 

 Exsic. Hep. Bor.-Amer. No. 147, 148, 149. 



20. R. natans L. Thallus large, purple, very narrowly 

 channeled above, the epidermis with numerous uniform air- 

 cavities beneath it, rooting toward the base and at length fur- 

 nished with large dark purple scales at the apex underneath; 

 divisions 0.8 1.2 cm. long, obcordate or obcuneate, broadly 

 emarginate at the thin apex; rootlets very long, usually smooth 

 within; inflorescence beneath the groove in one or two rows; 

 ostioles very short, purple ; spores angular, black, strongly pap- 

 illose. (Rictiocarpus natans Cor da.) 



Hob. Vegetating in summer in muddy bottoms of exsiccated pools, 

 etc., sometimes terrestrial. Canada to Gulf of Mexico. (Eu.) 



Bib Syn. Hep. p. 606, Hep. Europ. 172, Pro. Phil. Acad. 1869, p. 

 233-4. 



Delin. Lindenberg Monog. Eic. t. XXXI, XXXII. 



Exsic. Hep. Bor.-Amer. No. 144, 145. 



II. THALLOCARPUS LINDB. 



Thallus loosely spongy-reticulate, irregularly subpalmately 

 lobed, thin, ecostate, the epidermis not distinct. Rootlets not 

 papillose within, very long, interwoven. Fruit immersed in the 

 substance of the thallus. Calyptra crowned with the black 

 persistent style. Spores firmly united in fours into a sort of 

 coccus, finely reticulate and papillose. Name from Gr. thallos, 

 a shoot, and karpos, fruit. 



1 . T. Curtisii Aust. Thallus with somewhat imbricated, 

 flabelliform divisions which are palmately or incisely-lobed : 

 lobes crenate and obtuse, extremely thin and hyaline: spores 



