90 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



The endochrome in the greater number of species consists of two chromatophores 

 extending along the zone and sometimes partly over the valves. Sometimes, however, as 

 in N. hennedyi, N. lyra and N. humerosa, the bands are on the valves. Certain species 

 have four bands, others eight, and in one the endochrome is granular. (Mereschkowsky, 

 1. c., p. 9 et seq.) Pyrenoids are usually absent. On account of the diversity of the chro- 

 matophores, Mereschkowsky considers the genus not homogeneous. The difficulty of 

 arranging groups according to the cell contents, however, is so great that, for the present, 

 the species must be described by the usual characteristics of the valves and divided as 

 follows, according to Cleve, to the extent of employing the classification of all Naviculoid 

 forms as applicable, especially to the species of Navicula. Van Heurck's analysis includes 

 Pinnularia, Trachyneis, Diploneis, Caloneis, Neidium and Anomceoneis, which are here 

 separated, while N. lyra and N. hennedyi are placed in different groups, although they are 

 closely related. In other respects Cleve's divisions correspond, to some extent, to those of 

 Van Heurck. 



The genus Navicula at one time included the following: Dictyoneis, Pleurosigma, 

 Gyrosigma, Caloneis, Neidium, Diploneis, Frustulia, Trachyneis, Anomceoneis, Pinnularia 

 and Stauroneis, and few forms with a raphe escaped. For this reason the diagnosis of the 

 present genus is somewhat limited. Pleurosigma and Gyrosigma differ from Navicula in 

 their outline, Dictyoneis in the double stratification, Caloneis in the marginal lines, Neid- 

 ium in the median and terminal fissures, Diploneis in the horns, Frustulia in the terminal 

 nodules, Trachyneis in the stratification of the valve, Anomceoneis in the longitudinal 

 arrangement of the puncta, Pinnularia in the smooth costse and Stauroneis in the stauros. 



As the object of the present work is to aid the student of local forms in the identifi- 

 cation of species by the briefest methods, the further discussion of the reasons for classi- 

 fication will be left for his gratification in referring to the authorities on the subject. 



PUNCTATE CLEVE 



Valve elliptical to lanceolate; central nodule not stauroid or continued into lyriform 

 spaces; striae distinctly or coarsely punctate, in radiate rows. 



NAVICULA MACULATA (BAIL.) CL. 



Valve lanceolate-elliptical, with produced or sub-rostrate ends; axial area narrow, 

 wider near the ends and dilated to a rounded, transverse central area; strise radiate, 6 in 10 

 H, puncta, 7 in 10 M, in irregular, longitudinal rows. L. 90 to 120 /* (CL). 



Stauroneis maculata Bail. 



Navicula fischeri A. S. 



Blue clay. Along the coast, especially southward. 



PI. 24, Fig. 1. 



NAVICULA LATISSIMA GREG. 



Valve oblong-elliptical or elliptical-lanceolate, with sub-cuneate ends; axial area lan- 

 ceolate, widened in the middle to an orbicular space; striae radiate, 7 in 10 n, puncta, 11 in 

 10 , the median striae alternating with short striae along the sides. L. 50-150 n (Cl). 



Blue clay. Pavonia, N. J., artesian well. 



PI. 24, Fig. 3. 



