172 FRESH-WATER ALGJE OF THE UNITED STATES. 



22-24 }JL each way ; cells about 10 // ; each with a cruciform 

 marking on the surface. 



Small pond, near Bethlehem, Pa. 



Plate CLVII, figs. 9, 10, 11, three different forms ; fig. 11 

 having dropped one cell. 



Genus 45, SCEKEDESMUS, Meyen. 



Cells elliptic, oblong, cylindrical, ovate, or spherical, equal or 

 unequal at the ends ; often produced with a longer or shorter 

 spine. Cells most frequently laterally united, forming coenobia. 



Propagation by means of the repeated segmentation of the cell 

 contents into one or more brood families set free by the rupture 

 of the maternal cell membrane. 



Cells armed, or unarmed. 



SCENEDESMUS CAUDATUS, Corda. 



Cells oblong- cylindrical, each extremity obtusely rounded, 

 2-4-8 closely united in a simple series (rarely also in double 

 series) the outer cells of a series armed at each extremity 

 with a recurved spine. Length of cells about 22 yw. 



Kirchner makes the following varieties, which occur freely 

 with us also : 



Yar. TYPICUS, Kirch. Spines on the end cells only. 

 Yar. SETOSUS, Kirch. Spines on intermediate cells also. 

 Yar. HORRIDUS, Kirch. Spines on all the cells of a series. 

 Yar. ABUNDANS, Kirch. Spines in the middle of a cell, beside 



those on the ends. 

 Syn. Scenedesmus quadricauda, Breb. ; 8. quadricaudatus, Ealfs. 



Plate CLYI, figs. 11, 12, var. typicus; figs. 13, 14, smaller 

 forms 5 fig. 15, var. horridus. 



SCENEDESMUS ANTENNATUS, Breb. Yar. RECTUS, Wolle. 



Cells fusiform, 2-4 usually joined in a single series 5 rarely 

 a double series. Cells all somewhat curved and cuspidate 

 at the apex. 



Yar. RECTUS is separated from the typical form by its 

 universally straight cells and straight spines, not recurved. 



Diameter of cells, without spines, 13-14 yw. 

 Diameter of cells of variety, 14-16 //. 



Exposed moist white sand, Florida. Sometimes made 

 green with this variety. Have not identified the type-form ; 

 have quoted the diagnosis from Babenhorst's Flora Algarum. 

 Plate CLYI, figs. 16, 17. 



