26 Rhodora. [FEBRUARY 
occurs at Bermuda,' and on the Pacific coast near San Francisco, W. 
A. Setchell. It has fronds of a general orbicular outline, but more or 
less cleft and usually considerably plicate; the frond 30—40 y thick, 
parenchymatous in structure, the cells angular, of irregular form, the 
chromatophore similar in shape but considerably smaller; cells in 
cross section rounded, generally vertically elongate, 25-30 и high, the 
chromatophore occupying the middle part of the cell. ‘The frond is 
at first attached by fibrillar prolongations from the lower cells, but soon 
becomes free, and floats in quiet salt and brackish waters, the same as 
М. latissimum.: The texture appears to be firmer and the substance 
less gelatinous than in M. latissimum, and the dried specimen does 
not adhere very well to paper. 
In July, 1907, the writer found at Eastham, Massachusetts, along 
the shore of the “Salt Pond,” the expanded upper end of a long creek 
among the salt marshes, a plant which at first he supposed to be a new 
species, but which on the whole may better be included under M. orbi- 
culatum. It formed rounded rosette-like masses on the mud just 
above low water mark; attached by the center, a single individual 
being as much as 25 or 30 ст. in diameter of expansion. The folds 
in the frond were so abundantly developed that the appearance was 
that of a clump of many individuals, but in each case it proved to be 
one plant. In appearance, the cells were like those of typical M. 
orbiculatum, but in cross section the thickness of the frond ranged 
from 60 їп the lower part, to 16 «near the margin, and the cells 
throughout showed either a circular or a horizontally elongate section. 
Quite an area of the under side in the center of the frond was furnished 
with the fibrillar growths from the cells, which were here larger and of 
more irregular shape than in the rest of the frond. It may be character- 
ized as follows: — 
M. ORBICULATUM forma varians n. f. Fronde eximie plicata, sub- 
strato diu affixa; in sectione transversali 50-60 и crassa basin versus, 
prope marginem tenui, 16-20 x; cellulis in sectione plus minusve hori- 
zontaliter elongatis. 
Frond extremely plicate, remaining long attached to the substratum; 
in cross section 50—60 thick near the base, thin near the margin, 16- 
20 и; cells more or less horizontally elongate in cross section. — East- 
ham, Massachusetts, near low water on muddy shore of marsh creek. 
MALDEN, MASSACHUSETTS. 
1 Farlow in Farl, And, & Eaton, Alg. Am.-Bor, Exsicc., No. 173. 
