WISCONSIN PHYTOPLANKTON 



141 



The species has been bandied back and forth between Sphaerozosma 

 and SpoiidyJosiiim, largely because of the interpretation of the apical 

 elevation of the semicells. Since these are elevations of the semicell 

 apex and not apical processes the alga is a Spondylosium species. 



There has been even more dispute as to the identiy of the organism 

 ever since its description. This confusion has been increased by cer- 

 tain European investigators referring another Spondylosium species 

 to it; whereas in reality >S'. pulchrum is not found in Europe. Borge 

 has reviewed with great care all of the accounts of the species and 

 has come to the conclusion that most records of S. pulchrum should 

 be referred to the variety hrasiliense of Nordstedt (Wittrock & Nord- 

 stedt, Alg. Exs. No. 369. 1880), a variety that has long been over- 

 looked; and that the variety inflatum Wolle is in reality the type. 

 The variety hrasiliense is distinguished by the reduced apical eleva- 

 tion, more linear sinus, and especially by the compressed median 

 portion of the lateral margins in the vertical view. 



In certain cases the Wisconsin specimens do not have the polar 

 elevations in contact but the polar elevations are connected by very 

 short broad gelatinous bands. In one filament also the cells were 

 spirally twisted and not in a flat ribbon. 



3. Spondylosium moniliforme Lundell. PI. 87, Figs. 5-7. 

 Nova Acta Keg. Soc.Sci. Upsaliae 3 Ser., 8:92, pi. 5, fig. 16. 1871. 



Cells of medium size, radially symmetrical, length about twice to 

 one and a half times the breadth, very deeply constricted, sinus 

 widely open and with the apex rounded, isthmus narrow and some- 

 what elongate ; semicells subtriangular, with the ventral margins 

 rounded and the lateral margins convex; lateral angles broadly 

 rounded and the polar angle rounded or slightly flattened where the 

 cells are in mutual contact. Vertical view triangular, with the angles 

 broadly rounded and the sides strongly concave. Cell wall smooth. 

 Chloroplasts axial, with a small central mass and two broad plates 

 running to each angle of the cell; pyrenoid single and central. Fila- 

 ments not twisted, imbedded in a copious hyaline gelatinous envelope ; 

 area where cells are in apical contact narrow. (Facultative plank- 

 tont.) 



Zygospores unknown. 



Cells 30-32.5 fi long ; 20-24 ix broad ; isthmus 10 /x broad. 



Beaverdam (rr). 



Differing from other species in the radial symmetry of the vertical 

 view of the cells. 



HYALOTHECA Ehrenberg 1841. 



Cells united to form long filaments. Filaments not twisted but 

 generally enclosed by a copious gelatinous envelope that at times is 



