INFUSORIA. 73 
following interesting remarks with regard to the organs of locomotion in this genus, are also 
' taken from this work. 
“ In the small pools left by ebb of the tide near Cuxhaven, Dr. Ehrenberg remarked nume¬ 
rous little bodies, apparently similar to Navicula (Surirella) elegans and N. striatula ; but 
which, from their comparatively very great size and structure of lorica, were easily distin¬ 
guishable from the latter upon closer examination. One of these ribbed glass-like creatures 
was, besides its size, remarkable for its great mobility ; and Dr. E. Avas enabled to investi¬ 
gate its system of locomotion much more satisfactorily than he had hitherto done, in any of 
the genus. This organ he states was very different, both in form and size, to what he had 
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 animalcule y’^th of a line 
long, had twenty-four for every two plates, or ninety-six in the total; and anteriorly, at its 
broad frontal portion, four Avere visible. It is probable that this creature may form the type 
of a special group of the Bacillarise.” 
Navicula -. (PL 22, fig. 22.) This small species of Navicula Avith striate faces, is not uncommon 
in the infusorial stratum of Richmond, Va. 
1 ). Without transverse stride. 
Navicula -. (PI. 22, fig. 23, a, b.) This species is distinguished by having two grooves Avhich 
cross each other at right angles on the ventral face, presenting a cruciform appearance, and dividing 
this face into four equal portions, Avhich are without striae. It is a conspicuous species of many 
American specimens of fossil fresh-water infusoria, and is very common in the living state. I have 
found it in Neiv-York, Ouisconsin and Virginia. 
Navicula sigma. (PI. 22, fig. 24, a, b.) Smooth, carapace lanceolate on the straight side. 
Our figure represents a sigmoid species, found among marine algae at Stonington, Conn. 
A somewhat larger sigmoid species occurs in the infusorial stratum of Richmond, Va. 
Navicula? -. (PI. 22, fig. 25, a, b.) This very remarkable 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, 1. c. p. 427.) 
In addition to the American species of Navicula above described, Ehrenberg mentions the 
following as occurring in a fossil state at West-Point, viz : N. alata, nov. sp.; N. amphyoxys, 
and N. suecica. I 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. 
Geol. 1st Dist. 
10 
