1910.] NATURAL SCIENCES OF PHILADELPHIA. 459 



that we have here a sporangia! condition. This view would carry 

 with it an explanation of the comparative rarity of the diatom in the 

 gatherings of Mr. Terry. But on such an hypothesis, one would 

 expect to find, in this rich material, some indication of the process of 

 return to normal form. Nothing of this sort has yet been seen. 

 However, negative evidence answers no questions. Plainly enough, 

 a study of the life-cycle of this diatom is a desideratum. Not only 

 might such a study clear up the question of relationships within the 

 genus, — in Mr. Terry's form we have extra-generic characters, and 

 they may easily prove to be of great significance in solving the problem 

 of the genetic connections of Stauroneis, — but such a study will 

 necessarily be carried on with living material. 



Explanation of Plate XXXIV. 



Stauroneis Terryi, D. B. Ward. 



Fig. 1 — Complete frustule, girdle view, showing external ring. 

 Fig. 2 — Upper valve with subterminal depressions. 

 Fig. 3 — Lower valve. 



Amplification, 500 diameters. 



