110. Placynthium ] 30. PANNARIACEAE 171 



D. Apothecia with thalloid exciple 112. Pannaria 



C. Spores septate 



D. Lower cortex poorly developed 109. Massalongia 



D. Lower cortex wanting 110. Placynthium 



B. Under surface of thallus veined 108. Hydrothyria 



A. Thallus with green algal host cells 113. Psoroma 



* 



108. Hydrothyria Russell, Proc. Essex. Sust. 1:188-91. 1856. 



Thallus foliose, composed externally of a plectenchymatous cortex, one to 

 several layers thick, better developed above and under the apothecia; the medullary 

 area composed of densely interwoven hyphae; apothecia sessile, subterminal, with 

 proper exciple; hypothecium hyaline; paraphyses stout, several-septate, sometimes 

 branched toward the enlarged, brownish apices; asci clavate; spores 8, hyaline, 

 3-septate. 



The algal host is a short-chained form of Nostoc, and is scattered throughout 

 the medulla. 



1. Hydrothyria venosa Russell, Proc. Essex. Sust. 1:188-91. 1856. 



Thallus large, thin and brittle, lead-colored to brownish or blackish, loosely 

 lobed, the lobes fan-shaped, irregularly cut, obtusely crenate toward the ends; 

 bearing prominent brown, branched veins below; apothecia small to middle-sized, 

 0.75-2.5 mm. across, sessile and submarginal, the disk flat to convex, reddish brown, 

 the exciple becoming torn-dentate and disappearing; spores fusiform-ellipsoid, 

 24-32 X 7-8.5 fi. 



On rocks in mountain brooks, from New England to North Carolina, and re- 

 curring in California. 



109. Massalongia Koerb., Syst. Lich. 109. 1855. 



Thallus foliose, squamulose, or becoming almost crustose, smooth, resting upon 

 a well-developed, soon disappearing, black hypothallus, differentiated into a well- 

 developed, thin, plectenchymatous upper cortex of vertically extending, septate 

 hyphae, a thin irregular algal layer, and a more or less spongy medullary layer; 

 apothecia marginal, sessile, the disk flat to convex, the exciple thin, colored like the 

 thallus; hypothecium hyaline; hymenium hyaline or brownish above; paraphyses 

 unbranched; asci clavate; spores 8, hyaline to somewhat brownish, ellipsoid to 

 oblong-ellipsoid or spindle-shaped, 1-septate. 



The algal host is Scytonema. 



1. Massalongia carnosa (Dicks.) Koerb., Syst. Lich. 109, 110. 1855. 



Lichen carnosus Dicks., PI. Crypt. Br. 2:21. pi. 6, f. 7. 1790. Pannaria carnosa 

 (Dicks.) Rabh. 



Thallus composed of lobate, incised, suberect, often granular, imbricated, pale 

 to dark brown squamules; whitish below; apothecia small, 0.4-0.6 mm. across, 

 sessile, the disk flat to slightly convex, dark red to brown, the proper exciple thin, 

 usually lighter colored than the disk; spores oblong-ellipsoid to ellipsoid, finally 

 1-septate, 19-26 X 6.5-12 ju,. 



Among mosses on boulders, Yosemite Valley, California. 



110. Placynthium Ach.; S. F. Gray, Nat. Arr. Brit. PI. 1:395. 1821. 



Thallus foliose, squamulose or becoming almost crustose, smooth to more or 

 less rough, irregularly lobed, sometimes resting upon a thin, soon disappearing, 

 blue-black hypothallus, differentiated into a well-developed, plectenchymatous 

 upper cortex, an irregular algal layer and a thin, poorly developed lower cortex, 

 or appearing plectenchymatous throughout; apothecia minute to small or rarely 

 middle-sized, slightly immersed to adnate or sessile, the disk concave or flat to 

 more or less convex, the exciple thin, colored like the disk, sometimes disappearing; 



