100 DES.MIDS OF THE TfXlTED STATES. 



Prof. Bailey reports this species from South Carolina, 

 Georgia and Florida. 



X. CoLUMBiAXUM. Wolle. Plate XLY, figs. 10, 11. 



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

 constriction forming much ampliated. acute-angled sinuses ; 

 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 /(.: length So ja., without aculei. 

 Pond, Ocean County, New Jersey. 



X. BISENARIUM, Ehrlj. Plate XXYI. 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 aud margined 

 with pearly granules. 



Diameter 65-73 ia. 



West Point, N. Y. iBailey.) 



Ralfs suggests that this is the same as his X. Brebmonii. 

 The number of spines appears to be variable. Bailey and 

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

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

 cell. 



X. CEiSTATUM, (Breb.), Ealfs. Plate XXIY, 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 u. 



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



X. ASTEPTUii. Xord. Plate XXIV, 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 pt. without the spines. 



Bather rare ; quiet waters, Pennsylvania and New Jersey. 



