GrevillEj on New Diatoms. 87 



this feature. Sometimes it is every fourth^ at others every 

 third striae. In addition to these differences there is yet 

 auotlier, in Avhich the diatom under consideration agrees with 

 A. piilchra of Bailey C^Mic. Obs. in South Carolina, &c./ 

 p. 38; pi. ii, figs. 16 — 18), the strite 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. ulata. 



VOL. IX. /* 



