THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 119 



GRUNOWIA 



NITZSCHIA TABELLARIA GRUN. 



Valve rhomboidal, inflated in the middle; apices produced; keel puncta extend in 

 costse across half of the valve, 7 in 10 p.; strise transverse, about 22 in 10 ft. L. 20 /* 

 Dimerogramma sinuatum Thwaites. 

 Nitzschia sinuata var. tabellaria (Grun.) V. H. 

 Schuylkill River. Not common. 

 PI. 32, Fig. 7. 



SCALARES 

 NITZSCHIA SCALARIS (EHR.) WM. SM. 



Valve linear, with obtusely conical apices; costs transverse, extending more or less 

 to one-third the width of the valve, 3 or 4 in 10 n; striae, 9 or 10 in 10 n, punctate. 

 Length of valve quite variable, up to 480 p (Cleve) . 



A well-known form, abundant in salt marshes and more or less brackish water. 



PI. 33, Fig. 6. (To the right of the figure is an outline of the valve reduced one-third.) 



INSIGNES 



NITZSCHIA INSIGNIS GREG. 



Valve nearly linear or linear-lanceolate; apices broad, slightly produced, obtuse; keel 

 puncta extended into short costae, 4 or 5 in 10 n; strise about 14 in 10 p. Length variable 

 up to 400 p. 



Delaware Bay. 

 PI. 33, Fig. 8. 



BACILLARIA 

 NITZSCHIA PAXILLIFER (0. F. MUELLER) HEIBERG 



Frustules united in a filament, afterwards free; valve lanceolate with nearly central 

 keel; keel puncta, 7-9 in 10 ju; strise about 21 in 10 M- L. 110 M- 



Vibrio paxillifer O. F. Mueller. 



Batillaria paradoxa Gmelin. 



Nitzschia paradoxa (Gmelin) Grun. 



Brackish water or streams subject to its influence. 



PL 33, Figs. 13 and 14. 



Otto Frederick Mueller, in 1786, published at Copenhagen a work on "Infusorial Ani- 

 malcules," including a description of a Vibrio which he named paxillifer, obviously alluding 

 to the partially-extended frustules bearing at the end a tablet-like bundle. Two years 

 later, Gmelin described the same form as Bacillaria paradoxa, a name still used. Heiberg, 

 however, in 1863, placed the form under Nitzschia where it properly belongs and called it 

 Nitzschia paxillifer (O. F. Mueller). I have adopted Heiberg's name. 



Perhaps the most remarkable of all diatoms. Many species possess the power of mo- 

 tion, which, however, is evident only in the free frustule. In N. paxillifer, the movement of 

 the frustules occurs without the loss of continuity or adherence to each other, so that, while 

 at one time the adnate frustules form a narrow filament, like that of Fragilaria, at another 



