104 DESMIDS OF THE UNITED STATES. 



A. suBULATUS, Kg. Plate XXVII, figs. 11, 12. 



Semi-cells elliptic, larger tlian the preceding, with long, 

 subulate, erect or somewhat diverging spines. 

 Diameter 30-35 //. 



Ponds, Xew Jersey ; rather rare. I have somewhat modi- 

 fied the original diagnosis, by putting diverging for converg- 

 ing, and thus claim for this plant a distinct position. 



A. OEBicuLAKis, Wollc. Plate XXYII, figs. 15, 16. 



Very small, smooth, orbicular ; semi-cells united by a nar- 

 row isthmus ; aculei of the two semi-cells nearly parallel. 

 Diameter, without aculei, 12 yu. 

 Ponds, Mt. Everett, Mass. 



A. QUADEiDENS, Wood. Plate XXVII, figs. 17, IS. 



Broadly oval or suborbicular, a little longer than broad, 

 with the margin crenately undulate; semi-cells somewhat 

 reniform, at each end armed with a subulate, moderately 

 robust, acute, recurved, large spine ; cytioderm with a few 

 smallish tubercles arranged in three or four rows ; semi-cells 

 from the vertex acutely elliptical, with the margin crenate 

 and the surface sparsely warty. 



Diameter 19 //. ; length 30 //. 



Saeo Lake, N. H., (Lewis) Wood. 



A. INCUS, (Ehrb.), Hass. Plate XXVII, figs. 1-10. 



Cells minute, smooth, as long as, or longer than broad, 

 constriction a deep notch or sinus ; semi-cells with inner or 

 lateral margins turgid; outer, truncate; spines diverging, 

 subulate, acute; sporangium orbicular, spinous; spines 

 subulate. 



Diameter very variable 10-36 fi. 



Turned up frequently in every State in which explorations 

 have been made. 



A. ocTOCOENis, Ehrb. Plate XXVII, figs. 19-23. 



Smooth, about as long as wide ; the sinus produced by a 

 deep constriction, a wide notch. Semi-cells much com- 

 pressed, trapezoid, each angle terminating by one or two 

 subulate, acute spines ; the intervals between the spines con- 

 ca-^-e. Some specimens without reference to size, have two 

 spines at each angle. 



Diameter 16-25 /^. 



Not abundant, but scattered from Maine to Florida. 



