DOCIDIUM. 57 



I). MINUTUM, Ealfs. Plate LXI, figs. 29-31. Plate XIII, fig. 9. 



Slender, elongated, smooth, cylindrical, linear or slightly 



tapering, ends round ; 10-30 times longer than broad ; a 



single inflation, more or less prominent at the base of the 



semi-cell. 



Diameter 7-9 /<. , or more rarely 10-12 yw. 



Ponds, Florida, Massachusetts and New Jersey. 

 This minute plant is near a form described by Delponte as 

 P. rectum, but it has twice the diameter. Ralfs describes his 

 D. minutum, which has the same diameter as ours, only five 

 or six times longer than wide. Our forms vary greatly in 

 proportionate length and breadth ; the shortest, however, is 

 ten times as long as broad. They vary also much in thick- 

 ness and in the central inflation ; sometimes the constriction 

 is barely perceptible, and again marked by a strongly in- 

 flated border. The various forms frequently occur in groups, 

 and evidence specific relationship. 



D. TRIDENTULUM, Wolle. Plate XIII, fig. 10. 



Xear the preceding in form and structure but average 

 somewhat larger, and often granulate ; apices crowned with 

 a few prominent teeth, usually three in view. 



Diameter 12-13 //. 



Pleasant Mills, Brown's Mills, etc., New Jersey. 

 The inflation at the base of the semi-cells is more prominent 

 than is usual in D. minutum. 



D. COSTATUM, Wolle. Plate XIII, fig. 2. 



Fusiform, 7-8 times longer than broad ; slightly con- 

 stricted in middle ; inflated gradually from the base of the 

 semi-cell to about one-third the length, then gradually taper- 

 ing to the truncated, slightly dilated and dentate apex ; 

 margins with regular crenae, produced by twenty or more 

 distinct transverse costae or rib-like lines. 



Diameter, widest .part 25 /<., constriction 20 yu.. ends 

 15-17 //. 



Found by H. D. Kitchel in pond, Berkshire Mountains, 

 Massachusetts, 1882. 



The specimens which came under my observation were not 

 vegetative too old ; this species needs verification. 



D. VERTICILLATUM. (Triploceras verticiUatum ;, Bail. Plate XIII, 



figs. 1, 11. 



Cells large subcylindrical, with numerous whorls of small, 

 oblong, often tooth-like prominences ; 7-16 times longer than 

 broad ; ends with three bideutate diverging processes. 

 Diameter ordinarily 38-45 yw. 



