NO, 7 NEW SPECIES OF MARINE PENNATE DIATOM — CONGER 3 



always leaves a central (transapical) statiros-like area, in both valve 

 and girdle aspect. 



The shells are exceedingly delicate and gossamer-like and are not 

 amenable to conventional microscopic preparation; they disappear 

 completely in strong acid but withstand dilute hydrochloric and sul- 

 furic acids, which turn the chromatin material green but do not 

 digest it. The cells are very slightly silicified and are destroyed by 

 incineration. No mounting is possible by conventional methods. 



The vegetative cell population contains occasional spherical, trans- 

 parent bodies, peripherally pigmented with dense, essentially round, 

 but more or less irregular, pigment masses over a quarter or less of the 

 periphery of the sphere ; the remainder of the cell is clear. The 

 diameters of these spherical bodies range in size from about the length 

 of the frustules to up to twice this length. Occasionally the whole 

 sphere is filled with peripheral pigment bodies, obviously chromatin 

 material similar to that of the diatoms, although no "shell" forms are 

 distinguishable, or if present are collapsed. These pigment masses 

 appear to be either residues of former cells or perhaps parts of poten- 

 tial ones. They become quite numerous in old, stagnant, decadent cul- 

 tures. (Whether they are "auxospores," or some reproductive phase, 

 or a protective or degradational resting body in senile and decadent 

 cultures I am unprepared to conclude.) 



The cells are actively motile in new and healthy cultures, moving 

 in a mostly linear course, with few reversals; the movement in a 

 reversed direction is short (usually less than a cell length) before 

 forward motion is again resumed. The rate of movement is about 

 five to eight times the cell length in a minute. The cells in aging cul- 

 tures, even though they may appear otherwise healthy, are slower, 

 moving little or but a cell's length in a longer time. 



The cells are very strongly adhesive to the substrate in an Erlen- 

 meyer flask culture, making an even brown coating on the bottom of 

 the flask, and require somewhat violent shaking to loosen them ; in 

 contrast, for instance, with Phaeodactylum tricornutum, which is 

 either nonadhesive or readily stirred. Once detached from the sub- 

 strate, they quickly form in dark brownish, free-floating aggregates 

 or clumps that never adhere again to the bottom, but adhere strongly 

 to one another. 



This diatom is probably one that migrates in its natural benthic 

 environment in response to diurnal illumination, although there is no 

 observational evidence of this. 



In young, healthy cultures among large populations there are no 



