128 DESMIDS OF THE UNITED STATES. 



This species differs from all others of this genus in the form 

 of the cell, often twice as long as broad. Fig. 2 is very near 

 a form which Ileinsch denominated M. <in(jnlostnii. It is pro- 

 portionately shorter than the typical form of Ralfs, but other- 

 wise so near, it scarcely admits of separation. 



SECTION VI. Lobes horizontal, attenuated, bidentate. 



M. LATICEPS, Nord., 1869. (M, disputata, Wood, 1872.) Plate 



XLI, figs. 4. :>. 



Quadrangular, about as long as broad, subpinnatisected, 

 sinuses acute; terminal lobe nearly as long as the basal lobe; 

 both the lobes strongly attenuated ; the polar lobe into an 

 acute point and the other into an acutely bidentate apex ; 

 ends rounded or emarginate. 

 Diameter 160-212 yu. 



This species made its first appearance from Brazil and was 

 described by Nordstedt in 1869 in a scientific journal of 

 Sweden. Wood gave the same plant a new name a few years 

 later. The former has a claim of priority, hence should 

 stand. The plant varies considerably in size, and in the form 

 of the terminal lobes ; some are more rounded than others. 



It has been found in a large number of States. 



M. OSCITANS, Ealfs. Plate XXXVII, figs. 3, 4. 



Cells of nearly equal length and breadth ; the end lobe 

 separated from the adjoining lobe by a rounded or acute- 

 angled sinus; lobe horizontal, conical, their extremities 

 usually bidentate. One form has the ends of the terminal 

 lobe acute. The end lobes an- much shorter and narrower 

 than the others. Transverse view fusiform ; membrane 

 punctate. 



Diameter 150-160 yu. 



Bailey reports this species from Florida and Rhode Island, 

 but makes the measures much less. I have specimens from 

 Florida, Massachusetts and New Jersey. They were of the 

 given measures. 



M. piNNATTFim. Kg. . Half's. Plate XLI. figs. 7. 8, 9. 



Ends straight : semi-cells deeply constricted, lobes hori- 

 zontal, more or less fusiform with apices bidentate. 

 Diameter varies from 88-110 //. 



Somewhat like the preceding, but very much smaller, and 

 lobes not so swollen. 



Much more frequent than M. <n-itans. 



Some are found with the basal lobe wide (fig. 9); these I 

 have named, 



