28 Rhodora [JANUARY 
One of the most attractive of our Ænteromorphas both in habit and 
microscopically. ‘There are other species which occasionally have 
short monosiphonous branches, but in Æ. Hopkrikii nearly every 
young branch terminates in a monosiphonous series of considerable 
extent. A form is common in northern New England, growing 
largely on Cladoshora glaucescens, and also on rocks and shells, in 
rock pools. ‘This form is very slender throughout and the cells in 
the larger filaments have in a marked degree the net-like character 
found in Æ. clathrata; it seldom exceeds 2 dm. in length. In quiet 
bays another form occurs, sometimes reaching a length of over a 
meter ; in this form the cells are squarer than in the other, the fronds 
not so slender; it is common in southern New England. Europe. 
Harvey (1) 58. Farlow (1) 292. Collins (7) 246; (8) 44. Ulva 
Hopkirkii Farlow (4) 44. Collins (3) 310; (6) 78. Dame X Collins 
(1) 157. Martindale(1) 93. Britton (1) 401. Hay & MacKay (1) 
64. Exsicc. Phyc. Bor.-Am., 463. 
16. E. ERECTA (Lyng.) J. G. Agardh, Till Alg. Syst., part 3, 152, 
1882; De Toni, Syll. Alg., Vol. I, 133. 1889. Frond filiform, with 
numerous long, usually erect branches, more slender than the main 
filament; the ultimate ramuli of varying length, polysiphonous, the 
cells being symmetrically arranged in successive segments, similar to 
those of Polysiphonia; cells in main stem and branches in longitudi- 
nal and usually in lateral series. Plate 43, fig. 2. 
The most distinctive character of this species is found in the 
polysiphonous ramuli; in habit it is not unlike Æ. crinita, but the cells 
in Æ. erecta are usually more symmetrically arranged in the older 
parts of the frond, and more rectangular. It is not uncommon from 
New Jersey north, and appears to be a plant of exposed shores. 
Europe. Collins (7) 246: (8) 44. Æ. clathrata var. erecta Martin- 
dale (1) 93. Britton (1) 404. Ulva clathrata var. erecta Collins 
(3) 310. Exsicc. Phyc. Bor.-Am., 461. 
17. E. CLATHRATA (Roth) "Grev. Alg. Brit, 181, 1830: J. G. 
Agardh, Till Alg. Syst., part 3, 153, 1882; De Toni, Syll. Alg., 
Vol. I, 133, 1889. Frond filiform, cylindrical or compressed, much 
branched in all directions, the branches tapering from base to summit, . 
but not ending in a single series of cells; cells rectangular, usually 
longer than broad, always in longitudinal series, the chromatophor 
noticeably smaller than the cell. Plate 43, fig. 4, portion of surface 
of main filament. 
A common and variable species, differing from all the preceding 
except Æ. Hopkirkii and Æ. erecta in having a real system of branching 
of various orders; also in the chromatophor smaller than the cell, 
which, with the fact that the cells in adjacent series are usually 
alternate, gives a distinctly net-like appearance to the frond. It 
seems to be fairly common all along the Atlantic coast, and occurs 
also at Bering Island in the Pacific. Europe, West Indies, Tas- 
