86 MICROSCOPY FOR BEGINNERS. 



ened by small elevations. St. punctuldtum, Fig. 

 51. 



2. Cell not dumb-bell shaped ; with arms (a). 

 a. Cell triangular in end view, the angles toothed ; 

 arms in a cluster of about three on the end of 

 the cell, their ends toothed. St.furcigerum, Fig. 

 52. 



Fig. 51. Stanr&- Fig. 52. Stanra- Fig. 53. Stnnra- Fig. 54.-Stanrastruni 

 strum punctnla- strum furcigc- strum gracile. macnkerum. 



turn. rum. 



a. Cell triangular in end view, the angles prolonged 

 as narrow arms, the ends of which are three- 

 toothed ; surface roughened. St. ffrdcile, Fig. 53. 



a. Cell with six or seven radiating arms, their ends 

 three-toothed. St. macrocerum, Fig. 54. 



13. XANTHIDIUM (Figs. 55, 56). 



The cells bear near both ends a prominence or tuber- 

 cle that may be rounded and smooth, truncate, or appar- 

 ently encircled by small beads. 



1. Cell about twice as long as broad ; spines short, their 



ends irregularly toothed ; tubercles circular, beaded. 

 This is the only species with toothed spines. X. 

 armdtum, Fig. 55. 



2. Cell not twice as long as wide, each half somewhat 



kidney-shaped; spines in four or six pairs on each 



