XANTHIDIUM. 99 



Not SO frequent as the preceding, but not confined to any 

 particular localities. 



T. MNTJTTJS, D. By. Plate XXIII, figs. 7, 8, 9. 



Smaller than the preceding, only three times longer than 

 broad, membrane smooth. 

 Diameter 18-20 yU. 



Had this species from Florida, New Jersey and Pennsyl- 

 vania. 



T. GiGANTEXJS, Wood. Plate XXIII, fig. 6 ; Plate XII, fig. 1. 

 Yery large, oblong, three times longer than broad, with 

 the ends not'usually attenuate but broadly rounded ; suture 

 profound, linear; cytioderm irregularly granulately punc- 

 tate ; somewhat plicate at the base of the semi-cells ; cells 

 often contracted near the end. 

 Diameter 75 /«. more or less. 



Ponds, Pennsylvania and New Jersey. 



Genus, XANTHIDIUM, Ehrb. 



Cells single or geminately concatenate, inflated, profoundly 

 constricted ; semi-cells compressed, entire, spinous, protruding 

 in the center as a rounded, truncate, or denticulate tubercle. 

 Cytioderm firm, the spines with which it is armed, simple or 

 bi-tri-furcately divided at the ends. Zygospores globose, smooth 

 or spinous. 



X. ARMATUM, (Breb. ), Ealfs. Plate XXIV, figs. 1-4. 



Semi-cells largest at the base, about as long as broad, armed 

 with numerous, short, stout spines terminated by two, three 

 or more diverging points. 

 Diameter 62-140 //. 



Very variable in size. Fig. 1 is a finely developed form 

 from Mt. Everett, Mass. The other two are more usual 

 varieties found in all the States with which I had any com- 

 munication. 



This is the only species with spines divided at the apex. 

 Wood has two more, as X. c(rctiscon and X. coronatum, but 

 these must be separated from this genus, and placed with 

 Siaurastriim. 



The following have subulate spines: 



X. ACULEATUM, (Ehrb.), Breb. Plate XXVI, figs. 10, 11, 12. 



Spines subulate, more or less scattered ; central projection 

 truncate, obscurely dentate. 

 Diameter 62-70 //. 



