THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 63 



C. ventricosa is considered by some authors to be equivalent to C. affinis var. semi- 

 circularis Lagerst., Encyonema prostratum (Berk.) Ralfs, E. csespitosum Kuetz. and E. 

 auerswaldii Rab. H. L. Smith's Type Slide of C. ventricosa Ag. is said to equal C. affinis 

 Kuetz., but the specimens appear to me to be equivalent to C. ventricosa Kuetz. Cleve 

 unites many forms, including E. caespitosum, under C. ventricosa. 



CYMBELLA PROSTRATA (BERK.) CL. 



Valve semi-elliptical, obtuse at the apices, which are sometimes prolonged and turned 

 downwards; median line straight, terminal nodules distant from the ends; axial area nar- 

 row, central area rounded; strise in radiating, slightly curved lines, indistinctly punctate. 



Common in fresh water; occasional in brackish. 



PI. 18, Fig. 21 (represents a frequent variation). 



CYMBELLA PHILADELPHIA N. SP. 



Valve semi-elliptical-lanceolate, with rounded apices; ventral margin strongly gibbous; 

 terminal nodules distant from the ends; axial area broad, central area widened on the dor- 

 sal side; strise radiate, not curved nor of unequal length, indistinctly punctate, 10 in 10 ^ 

 on the dorsal, 8 in 10 M on the ventral side. L. 86 M- 



This form approaches Encyonema prostratum (Berk.) Ralfs, Schmidt's Atlas, PI. 71, 

 Fig. 7, but differs in the strise and the axial and central areas. 



Blue clay of Philadelphia. Rare. 



PL 18, Fig. 8. 



CYMBELLA TRIANGTJLUM (EHR.) CL. 



Valve semi^elliptical, with acute ends; median line straight; ventral side half the width 

 of the dorsal, with straight, slightly convex or concave margin; strise radiate, coarsely 

 punctate. 



Glosonema triangulum Ehr. 



Baker's Run, Willistown, Pa. 



PL 18, Fig. 24. 



CYMBELLA TTJRGIDA (GREG.) CL. 



Valve semi-elliptical, with acute ends; ventral margin gibbous; ventral side half the 

 width of the dorsal; median line straight; terminal fissures turned downwards; axial area 

 broad; strise radiate, coarsely punctate. 



Baker's Run, Willistown, Pa. 



PI. 18, Fig. 23. 



CYMBELLA TURGIDA (GREG.) CL. VAR. ? 



Valve lunate, with gibbous ventral margin; median line straight; terminal fissures 

 turned downwards near the ends; axial area lanceolate, strise radiate on the dorsal side, 8 in 

 10 n, punctate, 9 on the ventral side, closer at the ends where they are convergent. L. 65 ju. 

 Not a typical form. 



Willistown, Pa. 



PL 18, Fig. 12. 



CYMBELLA RHOMBOIDEA N. SP. 



Valve rhomboidal, with acute ends; dorsal part one and a half times the width of the 

 ventral; median line nearly straight, with terminal fissures turned downwards near the 

 ends; axial area broad, not widened in the middle, except slightly on the ventral side; strise 



5 



