72 
GEOLOGY OF THE FIRST DISTRICT. 
by a very delicate double line (canal ?) A similar structure is seen on several other species 
of Navicula, Cocconema and Gomphonema. The real orifices are shown at c, c, c, c, in our 
Fig. 16, b. Moving particles somewhat like those of Closterium may sometimes be seen near 
the extremities. In Fig. 17, a, b, PI. 22, I have copied from Ehrenberg, (Die Fossilen Infu- 
sorien und die Lebendige Dammerde, Berlin, 1837, PI. 1, fig. 19,) a sketch in which he 
represents the organs of motion, the stomach, etc. of this species. The reference letters hav¬ 
ing been omitted by the engraver of Ehrenberg’s plate, I have been obliged to insert them 
according to what I believe was their intended position. 
The following is a translation of Ehrenberg’s explanation of this figure. (See Fig. 17, 
PI. 22.) 
“ A living specimen of Navicula viridis, in which by the injection of indigo are distinctly 
to be seen: the stomach v, the two great spherical sexual glands s s, and the lamelliform 
extensions of the green ovarium, o' mouth opening, o' sexual opening ? a, a, a, a, four move¬ 
ment openings, p the pediform organs of motion. The visible currents on the body, both 
when creeping and at rest, are denoted by arrows.” 
Navicula viridula. Carapace straight, lanceolate, linear, very slender, truncate at the ends, flattened on 
one side, lanceolate and obtuse on the other, 13 to 15 strise in line, to -Jy line. Fmstulia 
viridula^ Ktz. (Linn. 1833, PI. 13, flg. 12.) 
Ehrenberg mentions this as one of the species detected by him among fossil infusoria from 
West-Point. Kiitzing’s figure does not allow me to determine with certainty, which of the 
various forms occurring at West-Point belongs to this species. 
Navicula -. (PI. 22, fig. 18.) This figure represents a panduriform species, very much contracted 
in the middle. It occurs in peat from a salt marsh near Stonington, Conn. 
Navicula -. (PI. 22, fig. 19.) This species occurs with the last, and is perhaps a state of it result¬ 
ing from its complete spontaneous division into two individuals by the contraction at the middle. 
Navicula -. (PI. 22, fig. 20.) This resembles the preceding very much, hut is a Ifesh-water 
species, occurring in ponds near West-Point, also in streams in Virginia. 
Navicula? striatula. (PI. 22, fig. 21, a, b.) I refer to this genus, with much hesitation, the very ele¬ 
gant and interesting species sho^vn by Fig. 21, a, 5. It is easily known by a set of peculiar and beau¬ 
tiful undulating ridges, represented in the figure, and which give to the margin of the form a ruffled 
appearance, in whatever position they are observed. One of the faces (a) is lanceolate, the other 
(b) is somewhat wedgeform, with both ends obtusely truncate. The lanceolate face shows a set of 
fine lines apparently proceeding from the ridges above referred to, and reaching nearly to the mid¬ 
dle line of the face. I have sometimes seen two individuals united laterally by their lanceolate 
faces, producing a very beautiful form: All the individuals which I have seen have been free, 
without pedicel, and when living, their spontaneous motions were very distinct. I have found it 
in a living state in fresh-water ponds and streams near West-Point; also in Mountain run, near 
Culpepper court-house, in Virginia; and I detected it in a fossil state among other fossil infusoria 
from Bridgewater, Mass. (See Figs. 6 and 7, PI. 20, of Hitchcock’s Final Report on Geology 
of Massachusetts.) 
In Pritchard’s History of Infusoria, I find two figures representing N. striatula, which 
leave no doubt that ours is the same species. (See Hist. Inf., PI. 3, fig. 137, 138.) The 
