64 GEOLOGY OF THE FIRST DISTRICT. 
Closterium moniliferum. Fig. 30, PL 21.) Semilunar, never straight, smooth, acute, and rounded at 
the ends, internal glands in the middle of the body arranged in a moniliform manner; green gra¬ 
nules in several rovrs, of 'W'^hich the three middle ones are most distinct. 
Specimens agreeing with the characters of each of the above species are common in this 
country. They do not, however, appear to be specifically distinct. They may be easily re¬ 
cognized by their smooth, green, crescent-like forms. 
Closterium trabecula. (Fig. 32? PL 21.) Straight, cylindrical, contracted in the middle, smooth, the 
ends truncate, glands scattered or in several series, numerous obscure bands, to i line. 
I have seen no figure of this European species, but I nevertheless venture to refer to it, 
the fine species represented in figure 32. This is the largest Closterium which I have seen 
in the United States. It occurs at West-Point, at Staten Island, and in Virginia. 
Its motions are quite distinct, the cavities containing moving particles very apparent, and 
what appear to be terminal openings may be easily seen. By the application of tincture of 
iodine, and then crushing the specimen under the compressor, starch globules may easily be 
detected. In crushing, the globules are often forced out at the terminal openings; and on 
relieving the pressure, are drawn back again. No rupture of a membrane at these points 
was perceived. 
Closterium digitus. (Fig. 33? PL 21.) Straight, oval, cylindrical, four or five times longer than 
broad, smooth, the ends very much rounded, sometimes showing traces of a spontaneous triple 
division, longitudinal bands often denticulate, to line. 
With this account may be compared Fig. 33, PL 21, which represents a species not un¬ 
common at West-Point, and which I have also seen in Rhode-Island, Virginia, and Ouisconsin. 
Its endochrome usually presents a central mass, from which several (ten) undulating ridges 
radiate to the carapace. It is a very elegant species. 
Closterium lineatum. (Fig. 34? PL 21.) Very long, acute, slightly arcuate, cylindrical, filiform in the 
middle, the ends truncate, and very acute (^Hres amincis")^ ridges distinct in form of smooth lines; 
often thirty times longer than broad, to i of a line. 
Compare with this Fig. 34, PL 21, which represents a species quite common in ponds near 
West-Point, and which also occurs in Virginia. The figure represents only one half of the 
excessively elongated body. In the living specimens, the endochrome shows distinct ridges. 
Closterium striolatum. (Fig. 35 ? PL 21.) Fusiform and arcuate, ends acute and truncate, ridges smooth, 
not deep, ten or twelves times longer than broad, yL line. 
Compare Fig. 35, PL 21, which represents a common species. 
Closterium rostratum, Ehr. Fusiform, slender, ends acute; setaceous horns about as long as the body, 
sometimes shorter. C. acus, Ktz. (Linn. 1833, fig. 81.) 
I suspect the species shown in Fig. 36, PL 21, is a young state of this species. I found it 
among Lemna minor, on Staten Island, New York. Fig. 36, a, shows an individual produced 
by spontaneous division, one portion of which is still imperfectly developed. 
Closterium tenue^ Ktz. “Corpusculis minutis lineari-lanceolatis, viridi hyalinis, transverse fasciatis 
acutis.” (See Linnsea, 1833, PL 8, fig. 78.) 
I find no notice of this species in the extract from Ehrenberg’s work, appended to Mandl’s 
