
9 
OF FILAMENTOUS, FRUTICULOSE, AND FOLIACEOUS LICHENS. 265 
Species 1. LP. candicans, Dub. 
This may be considered the type of a section of the genus, characterised by a 
whitish or grayish thallus. 
Speciinen 1.—LEIGHTON exs. 218 (sub Lecidea rimosa). (Syn. It is certainly 
not E. B. 1736, as LeraHTon quotes, but E. B. 1778.) On quartzose rock, Great 
Orme’s Head, Caernarvonshire. The spermogones are distinct, as minute blui®h 
or black points, sparingly scattered towards the periphery of the thallus. They 
are flattened or cone-like, wholly immersed, or nearly so. The spermatia are very 
short, rod-shaped bodies, bristling over the apices and sides of arthrosterigmata. 
SPECIES 2. P. circinatum, Pers., 
A comparatively widely-spread species, occurring in Europe, Africa, and Asia. 
Specimen 1.—Dereham Church, England, 1810; in Herb. Hooker, Kew (sub 
nom. Lichen candicans, Dicks.; Parmelia epigoea, Ach.) The spermogones are 
plentifully scattered among the apothecia. They.are seated on the warts of which 
the thallus is in a great measure composed. They are brown papille, which burst 
through the thallus, and become irregular, fiattish bodies, resembling deformed 
apothecia. The ostiole is seldom round and inconspicuous; it is, especially in 
the old state, more or less patent and stellate-fissured. The spermatia are rod- 
shaped, about amth long, and sth broad, seated on sterigmata about ith long, 
which are composed of only two or three linear irregular cellules or articulations. 
Specimen 2.—Clare Hall Bridge, Cambridge, Rev. H. Davies; also from same 
locality, coll. James Dauton, 1803,—both in Herb. Hooker, Kew. That portion 
of the thallus external to the region occupied by the apothecia is copiously covered 
with spermogones; they are seated on thalline warts, and are brown, irregular, 
papilleeform, sub-immersed bodies. 
Specimen 3.—Var. variabile, Pers.; Hepp. exs. 74 (sub. Placodium variabile) ; 
on old walls. The spermogones are pale, flat, brown, roundish spots, studded 
over the periphery of the whitish thallus. They closely resemble the spermogones 
of Lecanora subfusca, whose apothecia those of this variety of P. circinatum also 
resemble in outward aspect. The spermatia are oblong or sub-ellipsoid, almost 
atomic as to size. P. circinatum has frequently, intermixed with the ordinary 
or spermatiferous sterigmata, elongated, sterile, ramose filaments, like those which 
occur in many of the Parmelie. Nyianper has likewise noticed this fact; but 
he alludes to it as an abnormal and occasional condition only. I see no reason for 
regarding the occurrence of these hypertrophied sterile sterigmata in this species 
as exceptional, while they are regarded as normal in Ramalina and Parmelia. 
Indeed, I would lay down as a proposition, that there is a tendency in all spermo- 
gones whatever to the development of an elongated, hypertrophied, and sterile 
condition of the sterigmata. This is mostly seen in old spermogones, the sterig- 
