THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 79 



DICTYONEIS MARGINATA VAR. COMMUTATA CLEVE 



Valve four and one-half times longer than broad; cells of the valve in irregular, trans- 

 verse rows about 11 in 10 /x; marginal cells nearly equal, 6 in 10 p. L. 125 n. 

 Absecon, N. J. 

 PI. 20, Fig. 2. 



DICTYONEIS MARGINATA VAR. MAXIMA N. VAR. 



Valve with cuneate segments; marginal cells, 4 in 10 n; cells of the valve, 5 in 10 /u, 

 obsolescent in the middle and smaller; transverse stria?, 25 in 10 ju. 

 Atlantic Coast. Rare. 

 PI. 20, Fig. 1 (from a specimen found at Colon). 



TRACHYNEIS CLEVE (1894) 

 (trachys, rough, and neis (naus), named from the chief species) 



Valve more or less linear or linear-lanceolate. It appears to be composed of three 

 strata, one an interior, coarsely dotted, an exterior of fine puncta in longitudinal strife, 

 scarcely visible, and a median of transverse anastomosing costae forming irregular 

 alveoli. 



Chromatophores, two or four bands on the zone (Mereschkowsky). 



TRACHYNEIS ASPERA VAR. INTERMEDIA GRUN. 



Valve linear-elliptic; axial area a stauros widened outward and unilateral. Stria? 

 of the median layer of radiating rows of oblong alveoli. 



Along the coast. Not common. 



PI. 17, Fig. 15. 



The type form and its numerous varieties are quite ubiquitous. Very large specimens 

 occur in the Antarctic regions, especially in material from Ross Island, S. Victoria Land 

 (Shackleton Ant. Exp.). 



BREBISSONIA GRUN. (i860) 

 (named after Alphonse de Br6bisson, the distinguished French naturalist) 



Frustules stipitate; valve lanceolate; strise transverse in the middle, radiate at the 

 ends. Median area narrow, central nodule elongated, terminal fissures at a distance from 

 the ends. Valve with an outer finely punctate stratum. 



At one end of one valve in each frustule is found a conspicuous punctum, the plasma 

 pore of Otto Mueller, through which the frustule is connected with the gelatinous stipe, 

 analogous to the pore in Diatoma connecting the zig-zag frustules. 



Chromatophore single, lying on one girdle and passing over to each valve. 



BREBISSONIA BCECKII (KUETZ.) GRUN. 



Valve lanceolate, with sub-acute apices; striae, 3-4 in 10 n, not reaching the median 

 line. 



Blue clay. Very rare. Common in brackish water at Chestertown, Md. (T. C. 

 Palmer.) 



PI. 17, Fig. 7. 



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