HYDROTHYRIA. 167 



Trunks, and also rocks, not uncommon, but exceedingly rare 

 in fruit. In the extreme north b is the well-marked form, Bear 

 Lake (Bichardson), Hooker I c. 1823 ; Greenland ( Vahl), Th. Fr. 

 1. c. ; Islands of Behring's Straits, Wright ; extending also south- 

 ward, to Canada, Agassis; and New England; as also to the 

 Kocky Mountains (fertile), Herb. Hook. ; and Oregon, Hall. But 

 a is the more common state, especially southward, occurring 

 from New England to Virginia, Tuckerman ; in Illinois (fertile), 

 Hall ; in the low country as well as in the mountains of South 

 Carolina, Eavenel; in Alabama, Peters; and New Mexico, Fend- 



ler. The abundant fruit of a, as exhibited in the south of 



Europe, averages, in my specimens, l-2 mm - in diameter, reaching 

 3mm. j n SOII]e from the north of Italy collected by myself; and is 

 regularly scutellseform, with a plicate-rugose margin. These 

 features are equally well-marked and quite the same in Japanese 

 specimens ( Wright), important also as exhibiting the less regu- 

 lar and polyphylline thallus of the common United States lichen ; 

 and, like that, the thallus of these is only occasionally wrinkled. 

 In one of these more especially resembling the plant of the 

 United States, there is now a ring of white fibrils on the under 

 side of the exciple, and finally a downiness over the whole, thus 

 preparing the way for the otherwise altogether similar Illinois 

 lichen (Hall) in which the whole exciple is as hirsute as in many 

 Stictce. b is only known here, in a fertile state, in the specimen 

 from the Rocky Mountains (Herb. Hook.), in the dozen apothecia 

 of which, apparently always smaller, and much rarer in this 

 form of the species, all the mature ones (scarcely exceeding l mm 

 in diameter) are convex, and have excluded the thalline border, 

 which is represented by a crown of finger-shaped lobules, now 

 also visible at the edges of the lobes. There is some indication 

 of this overgrowth in my European specimens, the fruit of which 

 is occasionally also hirsute beneath (Bavarian Alps, Krempelhu- 

 ber) as in a. 



XXIX. HYDROTHYRIA, Russ. 



Apothecia biatorine. Spores cymbiform, quadrilocular, 

 decolorate. Thallus foliaceous, membranaceous, with a dis- 

 tinct, parenchymatous, cortical layer; a gommous one of 

 gonimia in short chains; and a medullary one of compact 

 filaments ; veiny beneath. 





