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its external characters; while T. clandestinwm, Fée, and T. catastictum 
of the present writer (Obs. Lich. 1. c. 6, p. 270) suggest not improbably a 
mediation of the difference in the spores. Leptotrema, Mont. & V. d. 
Bosch. in ML. Syl. p. 363 (Thelotr. Prevostianum, M. in Ann.) is, in this 
view, far less remote from Myriotrema, Fée, than was supposed; and the 
passage from colourless spores with entire spore-cells, to brown spores 
with at length murally divided spore-cells, takes place imperceptibly in 
one and the same series of most intimately related forms. 
In all from seventy-five to eighty species of Thelotrema, almost the 
whole from intertropical countries, have been indicated; the credit for 
by far the larger part being due to the labours of Nylander. A single 
well marked species (7. lepadinum) is common to Europe and North Amer- 
ica, but extends also within the tropics, and appears again (Nyl. Consp. 
Gen. Thelotr.) in austral regions. Several are only known as yet in the 
southern parts of the United States; where another occurs (TZ. szbtile) 
reaching northward to New England, and found also, according to Nylan- 
der, in tropical Australia. 
T. lepadinwm has only once occurred to me (on Birch) in the northern 
States, but is found in Arctic America (Hook. in Rich. Append. Frankl. 
Narr. p. 760) and in Oregon (Herb. Hook.). Southward it becomes more 
common (South Carolina, Mr. Ravenel; Louisiana, Hale; Texas, Mr. 
Wright) but the apothecia are smaller—We have however another 
northern species in 7. subtile, Tuck. Suppl. 1, 1. c. p. 426, described later 
by Nylander (xp. Lich. N. Caled.) under another name, which, found 
originally in Vermont (Mr. Frost) and the year after by myself in Vir- 
ginia, has also since proved to extend far southward. It isto these south- 
ern and at length semi-tropical regions that we are yet to look for the full 
exhibition of Thelotrema, as a North American genus. From the neigh- 
pouring island of Cuba, Mr. Wright has sent from thirty-five to forty 
species, and the number will probably be increased. A few of these are 
already known to occur within our limits. T. granulosum, Tuckerm. 
Suppl. 1, 1. c. p. 426, was found on Bald Cypress, in Louisiana (Hale). 
-——T. cavatum (Ach.) Nyl., a common tropical species, has recently been 
detected, on trunks, in Southern Texas (Mr. Ravenel).——7. Domingense 
(Fée herb., sub Ascidio. Nyl.) occurs in Mississippi (Dr. Veitch) and has 
lately been found in South Carolina (Dr. Mellichamp). From this scarcely 
differs, except in the rose colour of the interior of the thalline exciple, 
Ascidium rhodostroma, Mont. Guy. 1. c. (compare Nyl. in Prodr. Fl. N. 
Gran. 1. ¢.) to which may be referred specimens, finally, it is to be re- 
marked, shewing no trace of the coloration in question, from Louisiana 
(Hale).—T. monosporum, Nyl. (N. Gran. 1. ¢., Syn. N. Caled. p. 38) as 
determined by himself, is another discovery, on Bald Cypress, in Louis- 
jana, of the lamented Hale; and a form in which the apothecia are 
scarcely at all protuberant above the thallus, was collected in southern 
Texas by Mr. Ravenel.——That the great tropical assemblages, Thelo- 
