Sketch of the Infusoria of the family Bacillaria. 99 
before noticed in that genus. Instead of a snail-like expanding 
foot, long delicate threads projected where the ribs or transverse 
marks of the shell join the lateral portion of the ribless lorica, 
and which the creature voluntarily drew in or extended. An ani- 
malcule ;',th of a line long, had twenty four for every two plates, 
or ninety six in the total; and anteriorly, at its broad frontal por- 
tion, four were visible. It i is probable that me creature may form 
the type of a special group of the Bacillarie 
7. Navicula (Pl. 2, fig. 22.) This soni species of Navi- 
cula with striate faces, is not uncommon in the infusorial stratum of 
Richmond, Va. 
6. Without transverse strie. 
8. Navicula (Pl. 2, fig. 23,.a, b.) This species is distin- 
guished by having two grooves which cross each other at right angles 
on the ventral face, presenting a cruciform appearance, and dividing 
this face into four equal portions, which are without strie. It is a con- 
spicuous species in many American specimens of fossil fresh-water 
infusoria, and is very common in the living state. I have found it in 
New York, Ouisconsin and Virginia 
9. Navicula sigma. (Pl. 2, fig. 24, a,b.) Smooth, carapace lance- 
olate, sigmoid, not striate, linear, Micselnts on the straight side. 
Our figure represents a sigmoid species, found among marine 
Alew at Stonington, Conn. A somewhat larger sigmoid species 
occurs in the infusorial stratum of Richmond, Va. 
10. Navicula ? . (PL. 2, fig. 25, a,b.) This very remark- 
able form I detected among fossil infusoria, from the infusorial stratum 
of Richmond, Va. It is lanceolate when seen on one side; on . the 
other side it presents the curious outline shown in fig. 6. 
Note.—This may possibly belong to Ehrenberg’s new genus 
Zygoceros, which is described as having a compressed Navicula- 
shaped carapace; each end provided with two perforated horns. 
(See Pritchard, |. c. p. 427. 
In addition to the American species of Navicula above de- 
scribed, Ehrenberg mentions the fallenies as occurring in a fossil 
State at West Point, viz. 
N. alata, nov. sp. 
N. amphyoxys. 
N. Suecica. 
ole am, however, ignorant of their specific characters; I have 
met with many species besides those referred to in the present 
memoir, but omit them, as my present object is to present only 
the most interesting forms. 
