(74 ) 
of Phylliscum is also conformable to that of the typical Omphalaria, as un- 
derstood by Nylander; who does not recognize as belonging to the group 
any member of the Omphalariee of other authors, in which the collogo- 
nidia pass into chaplets. But the little cluster which exhibits this struct- 
ure (concatenate collogonidia) and which includes as well Omphalaria 
botryosa (Mass.) Nyl., as the North American O. wmbella (Collema, Nyl.) 
is in every other respect distinctly Omphalarieine. 
CoLLEeMA, Ach., Fr., is thus reached, in the view of Nylander, before 
we have left the marked group which other lichenographers, relying on 
the ensemble, are agreed in associating as Omphalariet. Collema num- 
mularium, Nyl. Syn. p. 103, as described by the eminent author cited, 
and as compared, in his figure, (t. 4, f. 9) with Omphalaria Girardi (f. 8) 
furnishes possibly other proof that anatomical structure may undergo 
marked modification, before the indications of habit, and these confirmed 
by the testimony of the microscopical fruit-characters, become at all 
obscure. 
But the question thus opened between keeping up natural groups by 
extending the limits of their definitions and thus subordinating modifica- 
tions of structure to evident conformity in habit, and the disregard of 
habit in view of conformity in anatomical details, is too wide for the occa- 
sion; and perhaps for the present condition of knowledge as to the real 
value, in the system, of such structural differences as separate Omphala- 
ria, Nyl., from Plectopsora, Mass. Suffice it to say that it is habit alone, 
in the last resort, which distinguishes Omphalaria, in the largest sense, 
from Collema, whether we look at the final advance in character of the 
former, or compare the most nearly related retrograde type of the latter. 
This type is Lempholemma, Koerb., which though comparable in part at 
least, in its reduced apothecia, with Omphalariei, and referred there by 
Stizenberger (Beitr.) differs yet in no important respect, either of ensem- 
ble or detailed structure from Collema, save only in its simple spores: the 
higher assemblage being largely characterized by a higher spore-structure. 
here understood (8. phylliscina, Msc.) found in Massachusetts (Mr. Willey). These 
are possibly new facts in the history as well of Synalissa as of Pyrenopsis, Nyl., 
to which latter group the species last named may rather be referable; but they 
will scarcely be considered as unsettling the systematic position of the lichens in 
question, as indicated by habit, and determined by other structure. 
1 It is interesting that the same question arises, probably, in Pyrenopsis, Nyl. 
There is, at any rate, nothing in the detailed description of Collema furfurellum, 
Nyl. (Lich. Scand. p. 28) to separate the plant from Pyrenopsis, except that 
‘ granula ejus gonima sunt moniliformi-disposita,’ or, more explicitly, occur ‘ sepius 
2—4 coherentia.’ Nor is this all. In the thallus of an original specimen of Py- 
renopsis fuliginea (Wahl.) Nyl., collected at Refsbotten, Finmark, by Wahlenberg, 
in 1802 (Herb. Fr.) I find no difficulty in observing gonidial chains of 4—5—6 
members; and the plant scarcely differs in any other respect from the descriptions 
But neither of these lichens can be regarded as quite at home in Collema! 
