I2(i DBSMIDS OF THE UNITED STATES. 



SECTION IV. Cells circular; semi-cells obscurely flve lobed, the end lobe the 

 broadest. 



M. DECEMDENTATA, STaeg. Plate XXXVII, figs. 5, 6. 



Suborbicular, granulate-punctate ; semi-cells distinctly 

 three lobed, or obscurely five lobed ; lateral lobes divided 

 by a small obtuse angled sinus into two lobelets, having 

 straight, truncate margins, angles slightly produced and 

 mucronate ; polar lobe broadly truncate, separated from the 

 adjoining lobe by a narrow linear sinus; apex broadly con- 

 vex, sometimes sinuate, lateral angles slightly produced and 

 mucronate. 



Diameter 83-100 /x 



Frequent in Florida ; have not found it farther north. It 

 differs from all forms described under this name, particularly 

 in size. The author, Naegeli, gives the diameter 40 p. Del- 

 ponte quotes subalpine forms at 50 p. ; and Lundell, the Sweden 

 plant also at 50 p., which is only half the size of our plant, but 

 omitting the measure, the description proves them identical. 



M. CRENATA, (Breb.), Balfs. Plate XXXVII, figs. 7, 8. 



Cells orbicular; semi-cells with five shallow lobes; end 

 lobe very broad, cuneate. end convex, or slightly sinuate on 

 the margin ; lateral lobelets nearly entire. 

 Diameter 75-85 yw. 



This species is met with only occasionally, Pennsylvania, 

 New Jersey, Florida. 



M. TRUNCATA, ^Corda), Ealfs. Plate XLIV, figs. 6-9. 



Orbicular; semi-cells five lobed; lateral lobes shallow; 

 end lobe very broad, truncate, angles bidentate ; lateral ones 

 incised - den tate. 

 Diameter 50-100 yw. 



One of the most common species of this genus. Variable 

 in size and the structure of the margins ; sometimes the lobe- 

 lets are obscurely toothed ; again very distinctly notched, and 

 another form is frequent with the angles drawn out into long 

 spine-like points, fig. 7. The truncate ends are usually more 

 or less rounded ; fig. 8 is a peculiar form with the ends perfectly 

 flat, and not detached from one another after multiplication 

 by division. 



M. CONFERTA, Lund. (M. granulata, Wood). Plate LXIV, fig. 12. 

 Broad elliptic, central sinus deep, narrow linear; semi- 

 cells five lobed, lobes and lobules always close ; polar lobe 

 subcuneate, more or less widened from the base to the end, 

 sides concave and apex convex but roundly emarginate in 



