DOCIDIUM. 51 



variable in different stages of growth, I put them all together, 

 and retain DOCIDIUM in preference to Pleurotaenium, as the older 

 name. 



D. ARCHERII, Delp. Plate XII, fig. 2. 



Cells smooth, cylindrical, about twenty times longer than 

 broad ; scarcely attenuated from the middle to the ends ; 

 apices broadly rounded or truncate; base of semi-cells with 

 one or two undulations. Chlorophyl usually arranged in 

 numerous small parallel bands. 

 Diameter 50-60 ^. 



Numerous in pond, Luzerne Co., Pa. 



D. CRENULATUM, (Ehrb.), Eab. ( Pleurotaenium nodulosum. D. By. 



Docidium nodulosum, Ealfs.) Plate XI, fig. 1. 

 Cell very stout, the thickened sutures forming a projecting 

 rim ; 8-16 times longer than broad, scarcely attenuated ; 

 regularly inflated at intervals so as to form an undulated 

 margin ; the basal inflation the most prominent ; ends sud- 

 denly contracted and truncated, furnished with three or four 

 teeth in view, below the margin ; cytioderm coarsely punc- 

 tate. 



Diameter 40-60 /v. 



Frequent in ponds from Vermont to Florida ; Minnesota. 



D. CLAVATUM, (Kg.), D. By. Plate XI, fig. 8. 



More slender than the last, suture not prominent, 16-24 

 times longer than broad, sensibly enlarged at the ends, more 

 or less clavate ; apices broadly rounded or truncate ; cytio- 

 derm firm, colorless, densely and irregularly punctate. 



Diameter, smaller forms 23-25 /*., larger forms 36-42 JJL. 

 Figure 8 has not the proportionate length. 



Pennsylvania, New Jersey, South Carolina and Georgia. 



D. TRABECULA, (Ehrb.), Naeg. (Docidium Ehrenbergii, Ealfs.) 

 Plate XI, figs. 2, 3, 4 ; and Plate XV, figs. 1-7. 



Long cylindrical, eight to twenty times longer than broad ; 

 tapering moderately from the center to the ends; apices 

 truncately rounded, not dentate; suture forming a sharply 

 defined rim, the inflation adjoining often having a smaller 

 one above it. Sometimes there is a contraction near the 

 apex ifig. 2). Cytioderm smooth. Zygospore globose, 

 smooth, surrounded by a colorless gelatinous envelope. 



Diameter 25-35 /Y. Length 180-450 /A 



Occurs frequently, and will probably be found in every 

 State in the Union. 



