P. T. Cleve: The Diatoms of Finland. 19 



remain certainly a large number of forms to be detected, which 

 will no doubt complete the system and fill up the gaps between 

 the larger groups. 



Raphideae. 



Piiinularia Ehb. 



The genus Pinnularia was established by Ehrenberg 1843 

 for the naviculaceous forms with smooth, strong stride. The ge- 

 nus was admitted by W. Smith and Rabenhorst, but rejected by 

 Kiitzing, Ralfs and Grunow. Pfitzer on the contrary retains the 

 genus, principally because of the nature of the striee (costse), the 

 slightly asymmetrical structure of the valves, and the arrangement 

 of the cell-content. 



As to the striae they seem, with the best objectives, to be 

 smooth, but according to Van Heurck x ) they have an excessively 

 delicate, and only with difficulty seen, punctation. Still the Pin- 

 nularia form a very characteristic group of closely allied forms, 

 and although there may be in several cases some difficulty to 

 decide whether a form should be classed as a Pinnularia or a 

 Navicula, I think it advisable to separate the Pinnularia from 

 Navicula. 



The determination of the species of Pinnularia is exceedingly 

 difficult, as the forms are variable and closely resemble each 

 other. In the litterature there exists a great confusion. The spe- 

 cies of Ehrenberg are in most cases impossible to identify, as the 

 figures are too little detailed and Ehrenberg has given the same 

 names to evidently different species, while on the contrary he of- 

 ten includes under one specific name very different forms. The 

 sketches and descriptions of W~ Smith and most older authors 

 are not sufficient. The figures in Donkins Brit. Diat. are better. 

 In the Atlas of A. Schmidt four plates with 204 figures are de- 

 voted to Pinnularia, and these figures are beyond doubt the best 



] ) Synops. des Diat. Belg. p. 225. 



