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lobes (‘lanugine tenuissima subtomentosi et versus basin fibrillis parvis 
obsiti, Ach. L. U.) and the part which remains velvety as compared with 
that which has become fleecy is now greatly reduced, it is evident that 
the distinction may well be expected ultimately to disappear in transitional 
forms; and such I regard a specimen before me, from Floerke’s herbarium, 
of his Coll. saturninum B tomentosum; and, no less, L. saturninum, A, 
sterile of Anz. Lich. Langobard. n. 9. Neither of these has the wrinkled 
upper surface of L. Hildenbrandti, but Arnold (Lich. Fragm. 1. ¢.) has 
referred the Italian lichen to the latter. The common plant of the United 
States belongs without doubt to this intermediate state, associated by 
Scherer and Arnold with what has been called L. Hildenbrandii, and by 
Anzi with LZ. saturninwm (Dicks.) and I refer to it also the cited lichens 
from Hawaii, and Japan, as, in part, those of the Himalaya. Only the 
specimens from the Rocky Mountains, and those from Arctic America, 
exhibit, with entire satisfactoriness, the velvety nap of the more northern 
plant; it is still not improbable that this condition of the under side 
may recur here in southern, and otherwise modified specimens; as it cer- 
tainly does, in great perfection, in an elegantly lead-coloured, fertile lichen 
from Sardinia (Herb. Duby). 
These notes will perhaps afford some satisfactory justification of the 
enlarged view of this species which I have been led to prefer. There are 
certainly reasons why even attempts at such larger judgments are most 
desirable. 
XXVI.—HYDROTHYRIA, Russell. 
Russell in Proceed. Essex Inst. 1, p. 188 (1856). Nyl. Syn. 1, p. 135. 
Stizenb. Beitr. 1.c.p.144. Leptogiisp., Russ. in litt., olim. Tuckerm. 
Lich. exs. n. 150. 
Apothecia pseudo-biatorina. Spore fusiformes, quadriloculares, 
incolores. Thallus foliaceus, strato corticali distincto; gonimo e 
collogonidiis moniliformi-subconcatenatis; filamentis medullaribus 
compactis; subtus venosus. 
In this type, remarkable alike in its characters and its habitat, Collema, 
Ach., which we found to reach its extreme of development in the Leptogia 
of more recent authors, may be said now to revert evidently towards 
Pannaria, and even Peltigera. With the general aspect of Leptogiwm 
proper, and so far less separable therefore, it should seem, than the 
Sticta-like Mallotia, Hydrothyria offers, at last, what is unquestionably a 
heteromerous thallus; and may thus be regarded as completing the evi- 
dence that Collemeine structure is, in the final analysis, inseparable widely 
from Pannarieine. The lax filaments, intermingled with gonidial chains, 
which represent the much confused gonimous and medullary layers in 
Leptogium myochroum, give place here to a compact medullary tissue, 
