36 FRESH-WATER ALG^ OF THE UNITED STATES. 



A. TRiANGULARis, Lagh. Plate LXI, figs. 14, 15. 



Sinus between the serai-cells wide, obtuse; semi-cells 

 triangular connected by a cylindrical isthmus, ends some- 

 what retuse in middle; angles subacute bearing a long 

 straight spine, either parallel or slightly converging ; senii- 

 cells in vertical view lanceolate- oval ; in lateral view sub- 

 circular. Membrane hyaline, in middle not thickened. 



Diameter, without spines, 25 ^ ; length 30 //. 

 Georgia. 



A. PACHYCEROS, Lagh. Plate LXI, figs. 13, 14. 



Cell small, constriction an acute-angled sinus ; semi-cells 

 suboval, sides convex, end arched, angles obtuse, each bear- 

 ing a firm spine, straight or slightly bent, diverging ; semi- 

 cells in vertical view oval ; in lateral view subcircular. 

 Membrane smooth. 



Diameter, without spines, 18 /< ; length 20 //. 



By an oversight this form was put on the plate ; do not 

 know it to have been found in the States. It is a Cuba plant. 



Genus, EUASTBUM. V. Des. U. S. p. 97. 



E. INTEGRUM, Wolle. Plate XXVII, figs. 18-22. 



The same is described as E. simplex Des. U. S. p. 106. 

 Since the publication of the diagnosis, F. Gay, of Mont- 

 pellier, France, is found to have anticipated the adoption of 

 the same name for another Hhiastrum form. Hence we sub- 

 stitute E. integrum for E. simplex. 



E. PECTINATUM, Breb. Plate LIY, figs. 10-12. 



Semi-cell three-lobed, terminal lobe dilated, usually en- 

 tire; lateral lobes broad, making the basal portion of the 

 semi-cell somewhat quadrilateral, horizontal, at each side 

 emarginate ; lateral view cuneate, with two swellings near 

 the base and one at the apex ; transverse view oval with 



three lobules on each side and one or imperfectly two at each 

 end. 



Diameter 40-50 yu ; length about 75 yw. 



Minnesota. A number of varieties of this species have 

 been described by specialists in different countries. The 

 present is not Ralfs' type-form, but a variety. It is 

 common in England, but hitherto not found here. 



