100 DESMIDS OF THE UNITED STATES. 



Prof. Bailey reports this species from South Carolina, 

 Georgia and Florida. 



X. COLUMBIANUM, Wolle. Plate XLV, figs. 10, 11. 



Cells about one-third longer than wide ; divided by a deep 

 constriction forming much ampliated, acute-angled MMUM-.X: 

 semi-cells oblong hexagonal, superior and lateral angles each 

 produced into a firm aculeus ; within the margins, four, often 

 indistinct, aculei ; end view more or less regular hexagonal, 

 each angle somewhat produced and surmounted by a firm 

 aculeus; within the margin are four aculei, the ends of which 

 often extend over the margin : ,cytioderm smooth. 



Diameter 60 yu. : length 80 yu., without aculei. 

 Pond, Ocean County, New Jersey. 



X. BISENARIUM, Ehrb. Plate XXVI. figs. 7, 8, 9. 



Cells in front view broader than long ; constriction deep, 

 sinus acute angled; spinous: spines subulate, marginal, gem- 

 inate ; central projection somewhat truncated and margined 

 with pearly granules. 



Diameter 05-73 /J. 



West Point, N. Y. (Bailey.) 



Ralfs suggests that this is the same as his X. Brebia^mii. 

 The number of spines appears to be variable. Bailey and 

 Ehrenberg's figures have six pairs of spines. Brebisson's, 

 eight; whilst some British specimens have ten to each semi- 

 cell. 



X. CRISTATUM, (Breb.), Raits. Plate XXIV, figs. 5-8. 



Semi -cells with a solitary spine on each side at the base, 

 the other spines geminate, in four pairs. Central protuber- 

 ance, short conical. 

 Diameter 40-55 i*. 



Pennsylvania, New Jersey, tSouth Carolina, Georgia, etc. 



X. ASTEPTUM, Nord. Plate XXIY, figs. 9, 10, 11. 



About one-fourth longer than wide ; semi-cells octangular- 

 oval, or truncate-triangular, with two diverging, somewhat 

 curved, subulate spines on each side, and two geminate spines 

 at each of the two superior angles. Cytioderm smooth or 

 punctate. 



Diameter 40-48 yu. without the spines. 



Rather rare ; quiet waters, Pennsylvania and New Jersey. ' 



