106 Rhodora [JUNE 
2, 7; Cushman, Zygosp. Desm., 1905, p. 225, pl. 7, figs. 7, Та. Cells 
of medium size, slightly longer than broad, nearly circular in general 
outline; deeply constricted, sinus linear; semicells five lobed, sepa- 
rated by linear sinuses; polar lobe broadening distally with nearly 
straight or slightly concave sides, apex concave with a median notch, 
the lateral angles bifid and a tooth at each side of the median notch; 
lateral lobes cuneate, about equal in size, divided twice dichotomously, 
the ultimate divisions emarginate; cell wall with a row of acute 
granules on either side of the sinus and interlobular incisions. Zygo- 
spore subglobose, with strong spines, simple or furcate at the apex. 
Length 152-155 p, breadth 135-148 и, polar lobe 36-43 y, isthmus 
15.5-21 p. Zygospore: length with spines 103-105 м, without spines 
75 p, breadth with spines 95 д, without spines 75 #. Me.: Orono (W. 
West); Bridgeton! N. H.: Pudding Pond, North Conway! Mass.: 
Amherst (W. West); Lake Quinsigamond, Worcester (Stone); Read- 
ing (Н. C. no. 734)! also with zygospores! К. I.: Near Providence 
(Bailey). The zygospores that I have observed had the majority of 
the spines simple, occasionally a few with the apices once furcate but 
none as much furcate as in Ralfs’ figure. The material from Read- 
ing had an abundance of zygospores associated with the empty semi- 
cells. 
13. MiCRASTERIAS ROTATA (Grev.) Ralfs, Ann. Nat. Hist., 1844, 
р. 259, pl. 6, fig. 1; Brit. Desm., 1848, p. 71, pl. 8, fig. 1a, (b?); Wolle, 
Desm. U. S., 1884, p. 109, pl. 34, figs. 1, 2; W. & G. S. West, Brit. 
Desm., 1905, p. 102, pl. 48, figs. 1-6. — Echinella rotata Grev., in 
Hooker, Br. Fl., 2, 1833, p. 398. Cells large, slightly longer than 
broad, general outline broadly elliptical; deeply constricted, sinus 
narrowly linear; semicell five lobed, polar lobe broadening distally, 
apex with a median notch, the angles with two spines, lateral lobes 
unequal, the basal ones smaller, each divided dichotomously three 
times, the ultimate divisions with spinose angles, interlobular sinuses 
narrowly linear, those between the lobules broader; no surface orna- 
mentation. Length 242 м, breadth 226 y, polar lobe 57 u, isthmus 
29 u. Me.: Penobscot River, near Orono (Harvey); Spencer Pond, 
East Middlesex (Н. С. по. 614)! N. H.: Pudding Pond, North Con- 
way! Mass.: Amherst (W. West); Lake Quinsigamond, Worcester 
(Stone); Westport (Н. C. no. 739)! К. I.: Wainskut Pond, North 
Providence (Bailey). This is one of our largest and showiest desmids. 
14. Micrastrerras Torrey Bailey, in Ralfs, Brit. Desm., 1848, 
