76 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



GYROSIGMA SIMILE (GRUN.) 



Valve slightly sigmoid, broad, with obtuse ends; raphe sigmoid, nearly central; trans- 

 verse striae, 15, longitudinal, 16-17 in 10 n (Per.)- 

 Pleurosigma simile Grun. 

 Gyrosigma balticum var. similis (Grun.) Cl. 

 Shark River, N. J. 

 PL 23, Fig. 4. 



(3) TRANSVERSE STRIDE MORE DISTANT 



GYROSIGMA ACUMINATUM (KTJETZ.) CL. 



Valve sigmoid, tapering to the sub-acute ends; raphe central; transverse and longi- 

 tudinal striae nearly equally distant, 17 or 18 in 10/* (Per.). 

 Frustulia acuminata Kuetz. 

 Port Penn, Delaware River. 

 PL 23, Fig. 5. 



GYROSIGMA STRIGILIS (WM. SM.) CL. 



Valve sigmoid, with obtuse ends; raphe doubly sigmoid; axial area rather wide; trans- 

 verse striae, 13, and longitudinal, about 16 in 10 ju. 

 Long Island Sound. Not common. 

 PL 23, Fig. 1. 



GYROSIGMA KUETZINGII (GRUN.) CL. 



Valve sigmoid, lanceolate, with sub-acute ends; raphe central, the central nodule 

 elliptical; transverse striae, 21-23, and longitudinal, 25-26 in 10 ju. 

 Pleurosigma spencerii var. acutiuscula Grun. 

 Pleurosigma spencerii var. kuetzingii Grun. 

 Common in fresh water. 

 PL 38, Fig. 12. 



GYROSIGMA SCALPROIDES (RAB.) CL. 



Valve slightly sigmoid, with obtuse ends; raphe nearly straight; central nodule ellip- 

 tical; transverse striae, 22, slightly radiate and more distant in the middle; longitudinal 

 striae, 29 in 10 M- L. 60 M- 



Common in streams. 



PL 38. Fig. 9. 



In PL 23, Fig. 6 represents a form more sigmoid. 



GYROSIGMA SPENCERII VAR. NODIFERA GRUN. 



Valve sigmoid, with obtuse ends; raphe central; central nodule obliquely elongated; 

 transverse striae, 17-18 in 10 n, curved in the middle of the valve, longitudinal striae, 22 in 

 10 M- L- 150 M- 



Blue clay. 



PL 23, Fig. 8. 



GYROSIGMA PROLONGATUM (WM. SM.) CL. 



Valve narrow, lanceolate, produced into beaks, curved in a contrary direction; 

 raphe central; transverse striae, 20-21 in 10 n, longitudinal closer. L. 140 p. 

 Along the coast, northward. 

 PL 38, Fig. 13. 

 I have not seen any specimens south of New England, but they will probably occur. 



