36 DESMIDS OF THE UNITED STATES. 



marshes, Florida. It is unlike the preceding in the absence 

 of the transverse sutures or rib-like projections ; in the 

 variableness of diameter and proportionate lengths. Diame- 

 ter of smaller forms 15-18 yw and of larger form 37 /^. The 

 smaller are 10-1-1 and the larger 7 times longer than broad. 

 Chlorophyl usually thrice interrupted. 



P. INTERRUPTUM, Breb. Plate Y, figs. 14, 15. 



Broad cylindrical, not constricted, 5-6 times as long as 

 wide, suddenly tapering, cuiieate near the ends, apices 

 rounded. Chlorophyl deep green, in matured plants inter- 

 rupted by three transverse pale bands ; cytioderm smooth. 



Diameter 38-50 /<., rarely only 16-20 /v. 



Habitat the same as the preceding, rather more frequent ; 

 readily distinguished by its transverse bands and cuneate 

 ends. 



P. CLOSTERIOIDES, Ralfs. Plate V, fig. 18. 



Cells narrowly lanceolate, 5-6 times longer than the 

 greatest diameter ; sensibly attenuated from the middle to 

 the rounded apices. Chlorophyl contents interrupted in the 

 center. 



Diameter 30-44 n* Ten times longer. 



Ponds, New Jersey, Pennsylvania and Minnesota. 



In its general appearance and in the arrangement of the 

 Chlorophyl, this plant has a strong resemblance to a C/oxtc- 

 rin>ii, but varies in being always straight and having the 

 opposite margins symmetrical. 



P. TRUNCATUM, Kalfs. Plate V, figs. 9, 10, 21, 22. 



Cylindrical, not constricted, 3-4 times longer than wide, 

 ends truncate, square. Zygospores smooth, spherical. 

 Diameter 11-12 ju. 



Ponds, northern counties of New Jersey. The Chlorophyl 

 is usually more or less interrupted in the middle, producing 

 a pale transverse band ; membrane smooth or finely punctate. 



P. MINUTUM, Cleve. Plate V, figs. 19, 20. 



Slender, cells 4-6 times longer than broad, sides straight, 

 ends rounded, without inflation, and without punctures. 

 Diameter 11-15 f-i. 



This small form, perhaps more properly a Calocylindrus, 

 (Plate XV, fig. 12), has not come under my notice. It is re- 

 ported by Bailey and Olney, from Florida and from Rhode 

 Island. The measures are taken from Babenh. Fl. Alg. The 

 figure in Ralfs, Br. Desmids, and referred to as belonging to 

 this species is certainly distinct and is a Docidium. 



