GrevillEj on Neio Diatoms. 
87 
this feature. Sometimes it is every fonrtli^ at others every 
third striae. In addition to these differences there is yet 
another^ in which the diatom nnder consideration agrees witli 
A. pnlchra of Bailey CMic. Obs. in South Carolina^ &c./ 
p. 38^ pi. ii^ figs. 16 — 18)^ the strise near the margin being 
punctate. The surface of the valve is undulate^ so that a 
portion only is in focus at one time, and the strise conse- 
quently appear to decussate obliquely in waving lines. I 
may add that, although I have seen a number of specimens, 
I have never observed one in the twisted state so common in 
A. alata. 
Vol. IX. 
