102 DESMIDS OF THE UNITED STATES. 



West. The former was published a year earlier than West's 

 name, heuce stands by right of precedence. 



This variety differs in having the spines at the superior 

 angles deflected horizontally and continuous with the margin 

 of the truncate or slightly convex ends of cell. 



Ponds and streams, Rochester, New Hampshire, and Am- 

 herst, Mass. 



Var. Canadense, Joshua. Plate XLIII, figs. 2, 3. 



Front and end views. Cytioderm minutely punctate, pos- 

 sessing no protuberance or granulation, resembling the var. 

 Minneapoliense in the possession of a fifth pair of spines, the 

 extra pair in the center of each semi-cell. 

 Pictou, Nova Scotia. 

 Diameter of cells (S. acul.) 45-50 ,". of all the varieties. 



X. RECTOCOENUTUM, Wollc. Plate XXV, figs. 10, 11. 



Cells as long as wide ; constriction linear, sinus sometimes 

 slightly excavated, and sometimes gaping ; semi-cells semi- 

 circular, finely punctate or smooth ; two rows of beads above 

 the central protuberance, the one with 6-10, and the other 

 under it with half the number ; another series of beads on 

 the base forming a ring around the isthmus ; ends broadly 

 rounded, nude ; basal angles with two pairs of aculei, or sub- 

 ulate spines ; the one horizontal, the other vertical ; trans- 

 verse view somewhat in the form of an hourglass, truncate, 

 crenate at the ends with two vertical aculei in the center. 

 Diameter without spines, 55-60 pi. 



Frequent in ponds, Mount Everett, Mass. 

 This species differs from X antilopceum in having the ends 

 of the cells bare, the upper pairs of spines not incurved nor 

 divergent, but erect, straight, attached to the sides, and 

 springing from the basal angle. It is also quite unlike that 

 species in the three series of beads, and in its transverse view. 



X. TETEACENTEOTUM, Wollc. Plate XXV, figs. 8, 9. 



About as long as broad, smooth, constriction deep, sinus ' 

 enlarged outwardly; semi-cells subreniform or subhexagonal, 

 base somewhat convex, ends broadly rounded ; basal angles 

 on each side armed with a pair of subulate spines ; central 

 protuberance low, over it sometimes a series of bead-like 

 granules. 



Diameter 33-37 pi. , without spines ; 60 pi- 'with spines. 

 Pond, Sussex Co., N. J. 



The form and character of this species is very near C anti- 

 lopceum, but it is smaller and bears only two pairs of aculei, 

 not four or six. 



