Naviculacca.'] infusorial ANiiiAi.cri.Es. 3 If? 



the internal and ventral, narrower than the other, the cxteiual or 

 dorsal ; secondaiy sides eqnal, transversely striated, the median 

 apertures of the margins approximate. 



This genus includes species distributed in the genera Syncyclia, 

 Cocconema, Navicula, and Pinnularia, of Ehrenberg's system. 



Its free unattached forms have an affinity, some with Epithemia, 

 others with Navimla and Ampliora, but differ from those genera by 

 their median ventral aperture, and by their unequal dorsal aspect. 

 Cymhella has also an affinity with the genera Gomphonema, Encyo' 

 nema, and Schizoncma, fi'om which also it may be distinguished by 

 the characters named. 



Cymbella Ehrenhergii r= N'aviada inequalis (Ehr.) — Large, un- 

 equally and broadly lanceolate; apices rather produced, and somewhat 

 obtuse; transverse striae pimctate, twelve in l-1200th (P. 3, f. 154.) 

 Length 1-21 6th. Berlin. Fossil, San Eiore. 



C. heteropleuia = Pinnularia heteroplcura (Ehr.) 



C. cuqmlata. — Small, rather wide in proportion ; apices produced 

 and slightly acute ; transverse striae fine, sixteen to eighteen in 

 l-1200th. Length l-576th. Fossil, Luncberg, 



C. obtusiuscula. — Small, elliptic, lanceolate ; apices not produced, 

 rather obtuse; transverse striae finef eighteen to twenty in l-1200th. 

 Length 1 -600th. 



C. yastroides. — Large, sublimate, unequal, thickened at the middle, 

 but tapering towards the obtuse ends ; transverse striae granular, 

 eleven to twelve in 1-1200. Length l-288th to l-216th (P. 17, 

 f. 18, 19, 20.) Fresh water, Germany. 



Yar. fh.j — Apices broadly truncate. 



C. maculata = Cocconema lunula (Ehr.) — Small, lunate, tapering 

 at each end ; obtuse ; primary side elliptic, truncate ; transverse 

 striae, twelve to thirteen in 1-1 200th. Fresh water, America. 



C. Helvetica. — Large, slender, elongate ; ventricose at the middle, 

 but tapering towards the rather obtuse extremities ; oblong on the 

 primary side, dilated at the middle, and tnincate at each end ; ti'ans- 

 verse striae fine, very beautifully granular ; thirteen to fourteen in 

 l-1200th. Length l-264th to l-240th. Thun, Switzerland (P. 17, 

 f. 24 to 28.) 



C. gracilis = Cocconema gracile (Ehr.) — Small, slender, lunate ; 



