1903] Collins, — The Ulvaceae of North America I9 
The specific distinctions are not always clearly marked, but that 
is to be expected in a genus of this extent, where the characters 
available for specific distinctions are so few. In the following 
arrangement J. G. Agardh's classification is pretty nearly followed, 
and a few more species are recognized than are allowed in Rosen- 
vinge's work. Though perplexing intermediate forms will undoubt- 
edly be found, it is thought that the type of each species will be 
found fairly distinct. 
KEY TO THE SPECIES. 
1. Frond flat, the membranes free at the margins but united between 
7. E. LINZA 
I. Frond of one to a few series of cells, not tubular 2 
I. Frond tubular 3 
2. Frond simple 12. E. PERCURSA 
2. Frond branched 14. E. CRUCIATA 
3. Cells not arranged in longitudinal 'series except in the very youngest 
parts 4 
3. Cells more or less in longitudinal series, usually in the greater part of 
the frond 9 
4. Cells of new generation in twos, threes and fours in the wall of the 
mother cell 2. E. FASCIA 
4. Mother cell wall not persisting after division 5 
5. Frond with short, spine-like ramuli, in addition to branches 
I9. E. ACANTHOPHORA 
5. Frond with more or less plentiful branches 6 
5. Frond simple or with a few proliferations i 
6. Frond with flattened rachis branching from the margin 
ra. E. MICROCOCCA var. SUBSALSA 
6. Frond filiform ; branches with contracted base, expanding upwards 
9. E. COMPRESSA 
7. Cells 10o-16pin diam.; frond usually inflated and constricted ; often of 
large size 6. E. INTESTINALIS 
7. Cells 4-8 p diam. ; fronds usually only 1-5 cm. long 
8. Frond 8-10 thick; cells 5—7 p diam. 8. E. MINIMA 
8. Frond 15-20 thick; cells 4-5 p diam. I. E. MICROCOCCA 
9. Frond simple, intlated and flexuous 3. E. FLEXUOSA 
9. Frond simple or with occasional proliferations; not inflated 10 
9. Frond regularly branched II 
10. Frond narrowly linear, strongly compressed IO. E. MARGINATA 
10. Frond filiform, 2-8 cells wide, tubular only in the widest parts; 
branches 2 cells wide I3. E. TORTA 
10. Frond filiform, tubular, of uniform diameter; of numerous series of 
squarish cells 4a. E. PROLIFERA var. TUBULOSA 
11. Frond beset with numerous short thorn-like branches 
5a. E. SALINA var. POLYCLADOS 
t1. Branches proliferous, similar to main filament 4. E. PROLIFERA 
11. Branches proliferous, of two or sometimes one series of cells 
5. E. SALINA i 
11. Branches of successive orders, tapering from base to apex 12 
12. Chromatophor filling cell 13 
12. Chromatophor not filling cell, giving a net-like appearance I4 
13. Ultimate ramuli short, spine-like, not monosiphonous 18. E. RAMULOSA 
13. Ultimate ramuli of a single series of cells II. E. CRINITA 
