136 WISCONSIN PHYTOPLANKTON 



Cells 12-18 [x long with apical processes, 8.5-12.5 /x long without 

 processes ; breadth 8.5-10 fi ; breadth at isthmus 4 /u, ; length of apical 

 processes 2.5-3.5 p.. 



Dutchmans (rrr), Lindy (rr), Tank (rrr). 



2. Onychonema laeve Nordstedt. 



Vidensk. Medd. f. d. naturhist. Foren. i Kiobenhavn 1869: 206, pi. 3, fig. 34. 

 1870; W. & G. S. West, Ann. Koy. Bot. Garden Calcutta 6: 224, pi. 12, figs. 8-10. 

 1907. 



Cells somewhat under medium size, breadth (without spines) one 

 and a half to two times the length, very deeply constricted, sinus 

 linear, with apex slightly inflated and outer margin widely open, 

 isthmus narrow; semicells transversely elliptic, with the ventral mar- 

 gin more rounded than the dorsal and furnished with two erect spine- 

 like apical processes that terminate in small knobs; lateral angles 

 rounded and each furnished with a single fairly long incurved spine. 

 Cell outline smooth and the wall without granulation. Vertical view 

 narrowly fusiform-elliptic, with poles bearing a single straight spine. 

 Filaments at times enclosed in a gelatinous sheath. 



Zygospores (of the variety micracanthum) spherical, furnished 

 with numerous small sharp spines (W. & G. S. West). 



Cells 16-17 fi long ; breadth with spines 31-36.5 fx, without spines 

 21-25 fi; breadth at isthmus 6 jtt (W. & G. S. West). 



Not found in the plankton of Wisconsin lakes. 



var. LATUM W. & G. S. West. PI. 86, Fig. 15. 

 Trans. Linn. Soc. 2nd. Ser. Bot. 5: 232, pi. 12, fig. 18. 1896. 



Cells broader than the type, sinus open and with an acute or 

 slightly inflated apex, apical margin of semicells with a truncate ele- 

 vation in the median portion, adjacent cells of the filament with their 

 truncate apical portions in contact; apical processes slightly diver- 

 gent. (Facultative planktont.) 



Cells 21-29 fi long with apical processes, 16-20 ju, without processes ; 

 breadth with spines 27-36 /a, without spines 21-26 ij. ; breadth at 

 isthmus 5-6 /x ; length of apical processes 3-4 fx ; length lateral spines 

 5-6 /i,. 



Beaverdam (rrr), Devils (sss), Diamond (rrr). Horseshoe (rrr). Little Doctor 

 (rrr), Soft (rrr), Sunday (rrr). 



Although the variety differs from the type in the length of the 

 lateral spines and nature of the isthmus the most striking feature is 

 the truncate apical elevation. All specimens found in Wisconsin 

 lakes can be referred to this variety. 



SPHAEEOZOSMA Corda 1834. 



Cells usually small and with the breadth generally somewhat 

 greater than the length. United to form permanent filaments by 

 short apical processes that lie on opposite sides of the apices of the 



