( 108 ) 
(J. Vahl in Th. Fr. 1. ¢.).——P. matrorum (Hoffm.) DC., is by no means 
so common with us as P. elegans ; and its range of variation is far less 
known. Of calcareous states I possess only a granulose, lemon-coloured 
lichen (Neosho river, Kansas, E. Hall) which scarcely differs from the 
very reduced var. citrinum, Nyl. (Moug. & Nestl. Crypt. n. 742) perhaps 
; . Slt 
hereafter to be given a separate place. Spores of this .~7mmm— 
P. teicholytum, DC., is wholly unknown as North American. We have 
yet an unquestionable member of the same stock from the lime- 
rocks of Kansas (Mr. Hall) which combines a white, areolate, finally lob- 
ulate thallus, with the habit of that of Lecanora muralis v. albo-pulver- 
wlenta, Scher. (Lich. Helv. n. 334) and scarcely middling-sized, zeorine 
apothecia (O™- 5-0". 9 in width) with small spores ({mmm.) and may 
take the name, with whatever ultimate rank, of P. galactophyllum.— 
P. eugyrum, Tuckerm. Suppl. 1, 1. ¢. p. 425, from lime-rocks in Texas (Mr. 
Wright) is a crustaceous, effigurate lichen, not wholly unlike in habit to 
Lecanora circinata, and comparable also with some conditions of P. callo- 
pismum (Ach.) Merat, from which it differs in its rusty-brown colour, &c. 
—We have indications of two interesting species of the group of effig- 
urate Placodia with ash-coloured thallus, from Western America. One of 
these, P. peliophyllum,! is an inhabitant of the precipices of the Yosem- 
ite valley, California. The other, referable perhaps, as a depauperate 
form, to P. variabile (Pers.) Nyl., was detected on rock-specimens from 
the Rocky Mountains (Dr. Hayden). 
To the cluster which includes P. cinnabarrinum (Ach.) <Anz., so 
familiar throughout the United States, is to be referred also the more 
conspicuous P. bolacinam, Tuck. (Lich. Calif. p. 18).——P. vitellinum is, 
in fact, in its best expressions, subsquamulose; and this indication of a 
higher than the granulose type of thallus finds its complement in the 
nearly akin but lobulate and radious P. crenulatum (Xanthoria, Th. Fr. 
Lich. Arct. p. 70. Lecanora, Nyl. Scand. p. 140) ‘intermediate in habit,’ 
says Th. Fries, ‘between’ P. marorum and P.-vitellinwm, which bas 
been found in Greenland by J. Vahl (Th. Fr. 1. ¢.) and also in Labrador 
(Herb. Krempelh.). P. luteo-minium, Tuck. (Lich. Calif. p. 18) is a 
granulose lichen of the west coast, belonging to the same cluster. The 
other species to be added to our list are all of the granulose section (Cal- 
lopisma, corresponding with Eulecanora in the next succeeding genus). 
—P. fusco-luteum (Sommerf., Th. Fr.) is, according to the latter 
author, found in Greenland (J. Vahl) and some scattered apothecia grow- 
ing with Mr. Wright’s specimens of the next species may belong to it. It 
1 Placodium peliophyllum (sp. nova) thallo crustaceo verrucoso cinereo-glauco, 
ambitu laciniato lineari-multifido; apotheciis (lat. 1-2™™-) sessilibus disco casta- 
neo, margine thallino integro demum flexuoso. Spore octone cllipsoidee polari- 
biloculares, incolores, longit. 0,014-21™™., crassit. 0,005-9™™. Not well comparable 
with any described species: but the specimens scanty. 
