350 Cushman : New England Saccodermae 



20. Netrium interruptum (Breb.) Liitkem. Penium interruptum 

 Breb. in Ralfs, Brit. Desm. 151.//. 25. f. 4. 1848. — Wolle, 

 Desm. U. S. 35. pL 5. /. 14, 15. 1884. — Netrium inter- 

 ruptum Liitkem. Beitr. Biol. Pfl. 8 : 407. 1902. 



Cells cylindrical, rapidly attenuate toward the obtusely rounded 

 apices ; chloroplasts four, two in each semicell, proximal ones in 

 each semicell cylindrical, distal ones conical, each with eight lon- 

 gitudinal plates, the free margins of which are entire. 



Length 172-320//: breadth 38-40//. 



Me. : Oldtown and Great Works {Harvey). N. H. : Inter- 

 vale ! Mass. : Lake Quinsigamond, Worcester {Stone). Pond- 

 ville ! Bridgewater ! 



Key to tlie New England genera and species of Saccodermae 



Saccodermae : Cell-wall unsegmented, without pores ; point of division of cells not 



fixed, and unknown previous to the actual division. 

 Cells elongate, cylindrical, unconstricted in the middle, forming loose filaments ; 

 cell-wall granular or spinose ; chloroplasts axile. (Gonatozygae. ) 



I. GONATOZYGON. 



Cells solitary, relatively short and mostly unconstricted. (Spirotaenieae. ) 

 One chloroplast in each cell. 



Chloroplast spirally twisted. 2. Spirotaenia. 



Chloroplast plane, axile. 3. Mesotaenium. 



Two chloroplasts (occasionally four) in each cell. 

 Chloroplasts star-shaped, radiating from a 



central pyrenoid. 4. Cylindrocystis. 



Chloroplasts with longitudinal ridges, the 

 edges of which are usually notched. 5. Netrium. 



I. GONATOZYGON 



Cell-wall densely granulate. 



Cells cylindrical, the apices slightly dilated. 1. G. monotaenium 



Cells cylindrical-subfusiform, the apices subcapitate. 2. G. Brebissonii. 



Cell-wall with small, short, straight, hair-like spines ; cells 



not dilated at the apices. 3. G. pilosum. 



Cell-wall with long, stiff, fairly stout spines. 4. G. aculeatum. 



2. S^IROTAENIA 



Chloroplast parietal, band-like. 



Cells large, cylindrical ; chloroplast broad, making 



8-10 close revolutions. 5. S. condensata 



Cells minute, fusiform ; chloroplast narrow, making 



about a single revolution. 6. S. parvula. 



Chloroplast axile, cristate, with several ridges, making 



about a single revolution. 7. S. obscura. 



