1914.] NATURAL SCIENCES OF PHILADELPHIA. 221 



Fig. 2 shows the accidental separation of two adjacent cells and the division 

 of the coinniissuro. 



Fig. 3 is a diagrammatic representation of the position of the commissure 

 near one side of the cell. The valves are frequently in close contact in the 

 middle, making the foramen bipartite. 



Fig. 4. — Represents the usual position of the commissure, although the dis- 

 tance from the edge of the valve is somewhat variable. Sometimes the com- 

 missure is in the middle of the side, but more frequently nearer one end. 



Fig. 5 is a valve view of the secondary valve as seen in the cell. 



Fig. 6 shows a form rarely found of a free spore much more developed than 

 the others and having the surface of the primary valve partly covered with 

 spines, somewhat as in C. wujhamii Br. Specimens of the latter in my 

 collection, however, show spores which are smaller, more circular, and with 

 the surface more evenly covered with spines. 



Fig. 7 represents two adjacent cells, as frequently seen, containing .spores 

 with their secondary valves opposed. 



The figures represent a magnification of 1,200 diameters. ^ 



^ I am indebted to Mr. F. J. Keeley for sketches from which some of the draw- 

 ings are made. 



