124 DESMIDS OF THE UXITED STATES. 



Sectiox III.— End lobe produced into four, more or less diverging, rigid, processes. 



M. AiiERiCAXA, ( Ehrb. \ Kg. Plate XXXVI, fig. 2 and Vars. 3-5. 



Semi- cells three lobed ; lateral lobes broad, cuneate. their 



margins concave, incised-serrate; end lobe broad cuneate and 



exserted, bipartite at the angles ; the subdivisions straight, 



narrow, minutely dentate at the extremities, end concave. 



Diameter 100-115 A'. ; length about one-third greater. 



The wide distribution of this species entitles it to the name 

 it bears. 

 There are several varieties, the one — 



Tar. EECTA, Wolle, (fig. 3). 



Is distinct in the margin of the polar lobe, which is not con- 

 cave and bisected, but straight with two small prominences. 

 Found it in a few localities in Pennsylvania and New 

 Jersey. 



Var. Heemaxjjiana, Eeinsch, (fig- 5.) 



Distinct in the angular intersections and regularly serrate 

 margins. 



Collected in Florida. It is not an exact counterpart of the 

 plant described by Eeinsch, but very near it. 



Var. SPixosA, Turner. Plate XLIX. fig. 30. 



A form not strictly from the United States, but near it, 

 may be introdirced. Mr. Turner describes it thus : A small 

 compressed form. About one-eighth less in length and 

 breadth than the type. Central portion of segments smooth ; 

 lobes ornamented with short stout spines ; the end lobe bear- 

 ing near its extremity a species of annular rugoso spinous 

 coronet. 

 Diameter 112 /^. ; length 136 ix. 

 Pictou, Nova Scotia. 



M. Mahabuleshwaeensis, Hobson. Plate XLI, fig. 10. 



This form stands in close relation with the preceding 

 species and varieties ; it is separated by having the lateral 

 lobes only once bisected, not twice. The margins are finely 

 serrated. 



Diameter 125 yu., more or less. 



Ponds, New Jersej , and eastern part of Pennsylvania. 



M. APICULATA, jMenegh. Plate XLV, fig. 3. 



Large orbicular or oblong, with the surface more or less 

 densely covered with mucros ; semi-cells five lobed ; lateral 

 lobes equal in size, not close, bisected; lobulets bifid, each 



