94 DESMID6 OF THE UNITED STATES. 



X. antelop^um, (Breb.) Kg. Plate XXIII, figs. 1, 2. 



Differs from the preceding in smaller size than the typical 

 X. fascieu/atiiiii, and in the reverse curvature of the lateral 

 spines. 



Diameter 45-50 u.. 



Yar. POLYMAZTJM, Nord. Plate XXI II, figs. .'3, 4. 



Unlike the true form in the series of bead-like granules over 

 the central protuberance. 



Yar. TRIQUETRUM, Lund. Plate XXII, figs. I, "2, .'}. 



Instead of an oval, end view, thi> is triangular, similar to a 

 form discovered by the author (Lund.) in Sweden, and to 

 another from Brazil, described by Dr. Nordstedt. 



The only locality for this variety, hitherto found, is a 

 trench near Quakertown, Bucks County, Pa. The other 

 forms may be called common. 



Yar. MlNNEAPOLIENSE, W'olle. Plate LI I, fig. 16. 



A new form from Minneapolis, Minn , possessing the pecu- 

 liarity of a fifth pair of aculei immediately over the central 

 protuberance and bead-like series of granules. 



X. RECTOOORNUTUM, Wolle. Plate XXII, figs. 10, 11. 



Cells as long as wide ; constriction linear, sinus sometimes 

 slightly excavated, and BOmetimes gaping; semicells semi- 

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

 the central protuberance, the one with 610, 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 

 subulate 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 centre. 



Diameter without spines, 55-60 fi. 



Frequent in ponds, Mount Everett, Mass. 



This species differs from X. anteloptcum 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. 



