OF THE FAMILY BACILLARIA. 125 



two transverse, somewhat elliptical bidentate, portions, the middle 

 portions longest. Occurs in ponds near AVest Point. 



8. Euastruni margaritiferum, Ehr. (Fig. 8, a, b, V\. I.) Body bi- 

 nary, cUiptical, each part semi-orbicular with the margin entire, ■^^- 

 to one twenty-fourth of a line. Ilcterocarpdla tetropthalma, Ktz. 

 Linn. 1833, PI. 19, fig. 67. 



Cm- species (fig. 8,) agrees })ret1y well wilh llio above descrip- 

 tion and witli Kntzing's figure. A figure given by Meyen in his 

 Pflanzen Physiologic, Vol. III. PL 10, fig. 31, apparently belongs 

 to this species also. 



The surface has a great number of minute^ hemisj)herical pro- 

 jections, disposed in a quincuncial order. It is possible that the 

 pearl-like appearance of these projections, when seen on the 

 empty carapace, may have suggested the specific name. I have 

 seen this species move quite distinctly, and have also seen in it 

 (as well as other species of EuastTum) groups of moving mole- 

 cules, as in Closterium ; sometimes indeed the whole cavity is fill- 

 ed with such particles. Meyen states that the species he repre- 

 sents (1. c. fig. 31, PI. 10,) contains globules of starch. 



This species is very common in the neighborhood of West 

 Point. I once found, in the spring of the year, in a small pool 

 caused by the melting of snow in a peat meadow, a large cloud- 

 like mass in the water, which, when touched, broke to pieces and 

 became diffused through the water. On examination, it proved 

 to be wholly made up of this species. I have found it in Rhode 

 Island, New York, Ouisconsin, and Virginia. 



9. Euastrum . (Fig. 9, PL I.) Binary, triangular, angles 



rounded, each corpuscle having several rows of minute points. Hab. 

 West Point. 



10. Eitastrum . (Fig. 10, PL I.) Binary, elliptical, each 



corpuscle having three pairs of long subulate spines. Hab. West 

 Point. I have met with individuals having the spines developed on 

 only one side. 



11. Euastruni . (Fig. 13, PL I.) Binary, corpuscles cor- 

 date at base, each having six pairs of short spines. 



This is a very pretty species which occurs at West Point. The 

 figure shows the position of two groups of active molecules. 



