IOWA ACADEMY OF SCIENCE 
61 
Achnanthoideae. 
Cocconeidaceae. 
Cocconeis. C. placentula Ehrenb. Abundant on old bladderwort in 
pond, Ontario. Buchanan. 
50. Naviculoideae. 
Naviculaceae. 
Navicula. Numerous species. 
Stauroneis. 
Amphipleura. 
Gyro sigma (Pleurosigma) 
Gonphonemaceae 
Gonphonema 
Cocconemaceae 
Cocconema. 
Amphora. A. ovalis. Kutz. Pond, Eagle Grove. Buchanan. 
Epithemia. 
Nitzschioideae. 
Nitzschiaceae. 
Nitzschia. Very common. 
Surirelloideae. 
Surirellaceae. 
Surirella. 
Class III. 
HETEROKONTAE. 
This class is one that has been segregated from the Chloro- 
phyceae to receive certain anomalous forms that seemed to have 
uncertain affinities. Of the three families created, two are found 
in the state. 
Order I. 
Confervales. 
KEY TO THE FAMILIES. 
Unicellular or filamentous; cells often elongate, uninucleate or sub- 
coenocytic, with several or many chromatophores ; cell walls firm and 
thick Tribonemaceae 
Plant body large and coenocytic, fixed, with well developed organs of 
attachment ; chromatophores numerous Botrydiaceae 
Family I. 
Tribonemaceae. 
This family as far as known is represented in this state by one genus 
only, Tribonema. 
1. Tribonema. 
