No. 588] POPULATION OF " BLANKET- ALG2E " 



755 



regularly as to quantity and time of occurrence and in- 

 cluded the following: 



Most of these were free but often Gomphonema, Cocco- 

 nema and Cymbella were in colonies attached by branched 

 or simple stalks to larger forms. Encyonema is found 

 end to end in colonies enclosed in long filament-like gelat- 

 inous envelopes. Navicula as well as stalked diatoms 

 sometimes covered the bodies of larvae and smaller crus- 

 taceans and also the cases in which the chironomid larvae 

 spent part of their time. Variation in occurrence of dia- 

 toms is apparently due to seasonal changes, which will 

 be considered later. 



Other algae were less constant, the most regular one be- 

 ing Closterium, which occurred in eight collections, show- 

 ing a number of species. Of the other desmids that ap- 

 peared, Cosmarium, Penium and Staurastrum were 

 usually in small quantities. Twice, however, Cosmarium 

 and Closterium both appeared in abundance, the first 

 time being in a permanent but shallow pool (7) where 

 Ulothrix predominated, and the second time in a shallow 

 but probably permanent roadside pool (G) covered with 

 Spirogyra. The Volvocaceae were represented by Volvox, 

 Eudorina, Pandorina, Sphcerella and Chlamydomonas. 

 Two Phaeophyceae, Dinobryon and Synura, and four Pro- 

 tococcaceae, Dictyospfarrinm, KirelincricUa , Protococcus 

 and Scenedesmus, added variety but did not appear fre- 

 quently. Peridinium, Pediastrum and Ophiocytium were 

 rare. 



The pools (L and F) that had the greatest variety in 

 desmids and kindred forms were also rich in diatoms. 



Tabellaria 

 Fragillaria 

 Meridion 



Cocconeis 

 Campylodiscus 

 Amphora 

 Pleurosigma 



Asterionella 



Diatoma 



Encyonema 



Cymbella 



Nitzschia 

 Odontidium 

 Cyclotella 



