40 DESMIDS f)F THE UNITFD STATES. 



C. MACiLEXTUM. Breb. Plate VII, fig. 6. 



Very loug eylindrica], slightly curved and reduced in 

 thickness near the ends, apices rounded ; 20-40 times longer 

 than the diameter. Cytioderm smooth, colorless, or yel- 

 lowish, usually with 1-4 transverse striae. Zygospore spher- 

 ical, smooth. 



Diameter 12-13 |v. 



Ponds, Pennsylvania, New Jersey. Not rare. 



C. Exsis, Delp. Plate VI, figs. ].3, 14. 



Cell elongate, about twenty times longer than broad, sub- 

 linear, or slightly attenuated from the middle to the apices ; 

 ends not curved ; cytioderm smooth. 

 Diameter 36 yu. 



Xot rare in ponds, Minnesota, Pennsylvania and New 

 Jersey. 



C. GEACILE, Breb. Plate VII, figs. 4, 5. 



Long cylindrical, 20-30 times as long as broad, nearly 

 straight, ends somewhat curved and slightly reduced in 

 thickness ; cytioderm smooth and colorless. Zygospores 

 according to Brebisson quadrangular, with rounded angles, 

 each of which bears a short spine. 



Diameter 5-6 //. ; zygospores 28-30 //. long ; 22 jx. broad. 



Xot infrequently intermingled with other desmids from 

 ponds, New Jersey, Penn.sylvania, etc. 



C. LAXCEOLATTJM, Kg. (C. tenue, Bailey). Plate IX, fig. 14. 



Cells semi-lanceolate. 6-10 times longer than broad, grad- 

 ually tapering, ends subacute, chlorophyl fillets several; 

 larger granules in a single series. Empty frond colorless 

 and destitute of striae. 



Diameter 40-50 yu. 



Pools, Florida; New York, (Bailey). Hundreds of speci- 

 mens in a gathering made by Prof. Cragin, Kansas. Stouter 

 and proportionately shorter than C acerosum. 



C. DiDYiroTOcuM, Corda. Plate IX, figs. 12, 13. 



Broad cylindrical, slightly curved, 6-12 times longer than 

 broad, slightly tapering towards the ends which are broadly 

 truncate, square; vacuole distinct containing many "danc- 

 ing granules;" cytioderm yellowish, finely longitudinally 

 striate. 



Diameter 30-32 yu. 



