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comparable, except in the size of the filaments, to that of Pannaria 
molybdea, and Peltigera; and the gonidia, less prone to the moniliform 
development, are rather crowded back into a true gonimous layer. But 
unlike Peltigera, with which the nerves or veins of the under side, — 
bundles, in both cases, of the medullary filaments, —so curiously associate 
it, the cortical stratum of Hydrothyria is for the most part continuous; 
and, in this respect, as in the not uncommon extension of this cortez, 
below, into a delicate pubescence, the plant may obviously be compared 
also with Nephroma. It is at the same time to be observed that there is 
nothing in the structure above described to exclude our plant from 
Leptogium beyond the veins of the under side; and it is in fact, in most 
other structural features, well-comparable with L. albo-ciliatum, Desmaz., 
to the neighbourhood of which, it should, as a Leptogiwm, be referable. 
H. venosa, Russ. 1. c. (Leptogium fontanum, Russ. in litt. olim. 
Tuckerm. Lich. ers. n. 150 (1857). Hydrothyria, Nyl. 1. ¢.) grows upon 
stones, under water, and fruiting in this situation, in mountain brooks of 
Vermont and New Hampshire (Russell) in Connecticut (Prof. D. C. Eaton) 
in New Jersey (C. F. Austin) and ‘‘in great abundance, on small pebbles, 
at the bottom of a clear brook,” at Big Trees, Mariposa, California (alt. 
6500 ft.) (H. N. Bolander) .——  Spermogones have not been observed. 
Fam. 6.—LECANOREI. 
Thallus crustaceus, aut effiguratus aut rarissime papilloso-ramu- 
losus aut uniformis, matrici adnatus, hypothallo diminuto 1. minus 
conspicuo. 
Indications of an atypical dissolution of the foliaceous into a more or 
less crust-like thallus have met us already in Theloschistes, and Physcia, 
and have proved as instructive as remarkable in Pannaria, but the pres- 
ent family is typically crustaceous; and, however now rivalling, or even 
approaching foliaceous types in its highest expressions, the difference of 
texture is not easily mistakable, and is evident also in the few fruticulose 
forms. So conspicuous indeed is, on the whole, the contrast between the 
effigurate Squamarie and Placodia of authors, and Lecanora proper, 
that the former, though differing in nothing but their lobation from the 
nearest allied granulose forms, have been separated generically by most 
recent writers — only Stizenberger returning here to the simpler concep- 
tion of Acharius. 
But marked as is the exhibition, in Lecanorei, of the reduction — car- 
ried finally to the utmost possible degree — of the Parmeliaceous thallus, 
the loss is more than made up by the variety and complexity of the fruit. 
This complexity has perhaps its typical maximum in Pertusaria ; which 
passes yet, on the one hand, with scarcely a break into Lecanora, while 
