56 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



striae crossed by longitudinal lines ..................... Caloneis 



striae oblique, median fissures in opposite directions ....... Neidium 



striae punctate and costate, median line with horns ........ Diploneis 



strife punctate; valves separated by septate plates ........ Mastogloia 



striae punctate, central area dilated into a stauros ......... Stauroneis 



striae punctate, area without stauros or horns ........... Navicula 



striae costate, not punctate ........................... Pinnularia 



ACHN ANTHER 



Frustules stipitate, free or parasitic. Valves cuneate, elliptical or suborbicular, dis- 

 similar, bent along the transverse or the longitudinal axes, the lower valve with a true raphe 

 and central and terminal nodules, the upper valve with a pseudoraphe or median line. 



Rhoicosphenia. Stipitate; valves with transverse puncta, bent along the transverse 

 axis, cuneate, with diaphragms at the ends. 



Anorthoneis. Free; puncta radiate; valves bent slightly along the transverse axis, 

 suborbicular. 



Cocconeis. Parasitic; valves elh'ptical, usually bent along the longitudinal axis; striae 

 punctate, transverse and longitudinal. 



Achnanthes. Stipitate; valves lanceolate or elliptical, bent along the transverse axis; 

 striae transverse, punctate; costae sometimes present. 



RHOICOSPHENIA GRUN. (i860) 

 (rhoicos, curved, and sphen, a wedge) 



Frustule in zone view curved; valves cuneate, dissimilar, the upper with a pseudoraphe, 

 the lower with a raphe. 



Chromatophore a single plate along both valves, and one of the inner walls of the zone. 

 Conjugation as in Gomphonema, with which it is generally associated in classification. 



RHOICOSPHENIA CURVATA (KTJETZ.) GRUN. 



Valve clavate, with rounded apex and base; lower valve with raphe, a narrow axial 

 area and slightly radiate, punctate striae; the upper valve with a narrow pseudoraphe and 

 parallel striae; a short diaphragm at the ends of each valve. Length usually from 15 to 25 /*, 

 but frequently of twice the size. 



Common in Crum Creek. 



PL 19, Figs. 25, 26, 27. 



ANORTHONEIS GRUN. 

 (anorthos, not straight) 



Valves dissimilar, the upper valve with an excentric axial area, the lower with an 

 excentric raphe. 



ANORTHONEIS EXCENTRICA (DONK.) GRUN. 



Valves orbicular, with radiating, punctate stria?, closer at the circumference, produc- 

 ing the appearance of a border. Axial area not reaching the ends. Frustules occur free on 

 the sands of the sea-shore. L. 25 to 50 ^. 



Belmar, N. J. 



PL 16, Figs. 30 and 31. 



