THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 77 



(4) STRIDE ALIKE, EXTREMITIES PRODUCED 



GYROSIGMA FASCIOLA (EHR.) CL. 



Valve lanceolate, attenuated into curved beaks turned in opposite directions; raphe 

 central, straight, except at the beaks; transverse striae, 22, longitudinal, 24 in 10 n (Per.). 

 New York Bay. 

 PI. 23, Fig. 9. 



FRUSTULIA AG. (1824); em. GRUN. dses) 



(frustulum, a small piece) 



Valves naviculoid, similar, usually free but sometimes enclosed in gelatinous tubes or 

 embedded in mucus. Median line between two thickened ribs. Central and terminal 

 nodules frequently elongated. Surface of valve with fine puncta in longitudinal and trans- 

 verse lines appearing hyaline under medium powers. 



Chromatophores, two, extending along the girdle. They differ from those of Navicula 

 in being separated from the wall in the middle by a hemispherical mass of protoplasm. 

 According to Pfitzer, each chromatophore is divided in the middle, allowing a connection 

 between the hemispherical mass and the central plasma mass. Schmitz states that the 

 chromatophore is thickened in the middle and contains a pyrenoid. 



In conjugation, two frustules form two cylindrical bodies which later become conical 

 and from which are formed the sporangial valves twice the usual size. 



FRUSTULIA LEWISIANA (GREV.) DE TONI 



Valve elliptical or linear, with rounded ends; terminal nodules elongated, at a distance 

 from the ends; striae, 24 in 10 /*. 



Port Penn, Delaware River. Along the coast. 

 PI. 17, Fig. 1. 



FRUSTULIA RHOMBOIDES (EHR.) DE TONI 



Valve lanceolate or rhombic-lanceolate, rounded at the ends; central and terminal 

 nodules short; striae, 20 in 10 M, sometimes coarser. 

 Common in fresh water. 

 PI. 17, Fig. 2. 



FRUSTULIA RHOMBOIDES VAR. AMPHIPLEUROIDES GRUN. 



Valve rhombic-lanceolate; central and terminal nodules elongated; median line some- 

 what excentric. 

 Blue clay. 

 PI. 17, Fig. 3. 



FRUSTULIA RHOMBOIDES VAR. SAXONICA (RAB.) Dfi TONI 



Valve smaller than in rhomboides, with somewhat produced ends, closer median ribs 

 and rounded central nodule. 

 Fresh water. 

 PI. 17, Fig. 6. 



FRUSTULIA VULGARIS (THWAITEs) DE TONI 



Valve elliptical-lanceolate, with rounded or sometimes sub-rostrate ends; central and 

 terminal nodules slightly elongated; striae delicate, closer at the ends. Frustules at first 

 in gelatinous tubes. 



Colletonema vulgaris Thwaites. 



Fresh water. 



PI. 17, Fig. 4. 



