1903] Collins, — The Ulvaceae of North America 17 
nearly circular, 14-18 u high. Plate 41, fig. 18, cross section; fig. 
19, Surface. 
Apparently not uncommon in quiet waters, especially in ditches in 
marshes, where the water is sometimes brackish rather than salt. At 
first it is attached to various objects, but soon becomes loosened and 
floats freely, sometimes in such abundance as to quite fill a ditch 
from bottom to surface. It appears in spring, and continues, chiefly 
in the floating state, through the summer. ‘The color is a quite rich 
green in the young plant, usually paler in the older, floating indi- 
viduals. "The arrangement of cells varies in plants from the same 
locality, and even in different parts of the same frond ; in some cases 
the arrangement of cells in twos and fours is very like M. guaternarium 
but the New England plant probably is all M. /a£issimum. The cells 
are usually said to be vertically elongate in cross section; but this is 
true only in a general way, as individual cells, and sometimes a con- 
siderable proportion of the whole, have their longer axes parallel to 
the surface of the frond; indeed, the shape of the cells, whether 
seen from above or in cross section, is liable to vary in any species 
of Monostroma, or in different stages of growth of the individual. 
From Maine to Florida; Washington and Alaska; shores of Europe, 
Africa, New Zealand. Dame & Collins (1) 158. Collins (4) 341; 
(8) 44. Exsicc. Phyc. Bor.-Am,, 14. 
9. M. QUATERNARIUM (Kütz.) Desmaz., Plantes Crypt. de France, 
Nouvelle Série, 603 ; Wittr., Monogr., 37. 1866: J. G. Agardh, Till 
` Alg. Syst., part 3, 98, 1882 ; De Toni, Syll. Alg., Vol. I, 100, 1889. 
Frond at first attached, soon becoming free, soft and delicate, irreg- 
ularly lobed and folded, 20-23 yw thick ; cells rounded, when actively 
dividing set closely in threes and fours within the mother cell wall ; 
in cross section semicircular or oval, 15-17 p high. Plate 41, fig. 16, 
cross section ; fig. r^, surface, 
As was noted under M. /atissimum, that species is very near M. 
guaternarium, and as far as New England specimens are concerned. 
it is impossible to draw the line. Specimens from California, how- 
ever, all as far as seen distinctly show the arrangement in threes and 
fours, and more plainly than do any eastern specimens. 
Besides occurring in salt water at Santa Cruz, California, it is found 
in quite fresh water in the interior of the state, at Santee, by Miss 
Minnie Reed, and was collected by Dr. Sereno Watson at 2000 
meters elevation in the Diamond mountains, Nevada. It occurs in 
various parts of Europe. I am indebted to Dr. George T. Moore of 
the U. S. Department of Agriculture for the opportunity to examine 
an authentic specimen of Uva merismopedioides Wood, collected by 
Dr. Watson in connection with the U. S. Geological Exploration of 
the Fortieth Parallel. — It is undoubtedly M. guaternarium, and as 
the cells are actively dividing, the quaternate character is very marked. 
Anderson (1) 218. Ulva merismofedioides, Wood (1) 182. Exsicc. 
Phyc. Bor.-Am., 567. 
