RHAPHIDIUM. 197 



/ 



NEPHROCYTIUM AGARDHIANUM, Naeg. 



Cells 2-4 times as long as wide, arranged in families of 

 4-16, enclosed in a thin tegument ; families 2-3 times as long 

 as broad. 



Diameter of cells, variable, 3-7 //. 



Not infrequent in ponds with Desmids, etc. 



Plate CLXIII, figs. 12, 13, mature cells ; figs. 14, 15, 17, 

 younger forms. 



NEPHROCYTIUM NAEGELII, A. Br. 



Cells oblong, two or three times longer than broad ; two, 

 four or eight enclosed in a rather wide subspherical tegu- 

 ment. Cells bright green, at length set free by the dimuence 

 of the membrane. Length of cells 33-38 ^ before division. 



Syn. Oocystis Naegelii, A. Br. 



Between the two genera Nepkrocytium, Naeg., and Oocys- 

 tis, Naeg., there appears too slight and uncertain a distinc- 

 tion for separation. Neither is likely to stand eventually. 

 They have the appearance of intermediate life conditions, 

 which are not yet fully understood. 



Genus 62, BHAPHIDIUM, Kg. 



Cells fusiform, or cylindrical, generally very gradually cuspi- 

 date or acuminate at the ends ; rarely obtuse, straight or vari- 

 ously curved, single, geminate, or fasciculately aggregate, decus- 

 sate in the center, or radiately conjoined, rarely two laterally 

 united at the end ; other cells free. Tegument thin, smooth. 

 Contents green, very finely granular, furnished with a central, 

 or rarely lateral, transparent vacuole. Division of the cells only 

 in one direction. 



EHAPHIDIUM POLYMORPHUM, Fres. 



Cells single or from 2-16 or more associated in fascicles, 

 acutely cuspidate at each end, straight or variously curved ; 

 usually of yellowish green color. Cells 12-25 times longer 

 than broad. 



Diameter, 1.5-4 //. 



The following forms may be selected, as distinct varieties : 

 a.--Var. ACICULARE, A.Br. 



Straight or slightly curved, attenuated at each end, 15-20 

 times longer than the diameter. 



Sometimes in large numbers in stagnant waters. 

 Syn. Closterium Griffiihii, Berk. 

 Plate CLX, figs. 22, 23. 



