244 
GEOLOGY OF THE FIRST DISTRICT. 
from its vast extent, the beauty of its species, and from its belonging to the marine tertiary 
formations. All other American fossil infusoria yet discovered are of fluviatile origin, and of 
the most recent date. 
I have already pointed out the striking correspondence between the fossils of the infusorial 
stratum of Virginia and those of Oran in Africa. This is shown by the occurrence of vast 
quantities of various species of Coscinodiscus and Actinocyclus, with Gaillonella sulcata ? 
etc. Believing that it will be of great interest to geologists both at home and abroad to trace 
out this correspondence of the fossils of regions so far distant, and of beds which are at present 
referred to different epochs,* I have added to my plate third, a number of figures of siliceous 
bodies not before described, found in the infusorial stratum of Virginia. The following is a 
brief account of these bodies. 
In PI. 42, fig. 24, a, b, c, are shown different views of small siliceous bodies, which are 
quite frequent in the infusorial deposits both of Richmond and Rappahannock cliffs. They 
consist of a concave rhomboidal body, formed of open work, or with large perforations, and 
having at the extremities projecting spines. These belong to the genus Dictyocha of Ehren- 
berg, several species of which occur at Oran, Caltasinetta, &c.t 
PI. 42, fig. 25, shows a siliceous ring with projecting spines ; it is possibly a fragment of 
the preceding. 
PL 42, fig. 26, shows a circular ring, connected with a concentric hexagon by six rays pro¬ 
ceeding from the angles of the hexagon. The spaces within the hexagon and below the rays 
are perforations. It is another species of Dictyocha. It occurs occasionally among fossil 
infusoria from Richmond and Rappahannock cliffs. 
PI. 42, fig. 27, shows a curious fragment, apparently siliceous, having a campanulate form 
with a projection at the apex, and pierced with large holes. Fig. 28 shows an ovoid body 
perforated by similar holes. Of the nature of these curious fossils, I am entirely ignorant. 
They occur with the preceding. 
PL 42, fig. 29, shows a triangular binary siliceous body, resembling some of the fluviatile 
species Euastrum. The surface is covered with minute dots, some of which form lines lead¬ 
ing from the centre to the angles. Perhaps this belongs to Ehrenberg’s genus Triceratium, 
of which species occur fossil at Oran, and living in Cuxhaven. 
In PL 42, figs. 30 to 35 show siliceous bodies which are quite abundant with the preceding 
forms, and which I suspect are spiculae of marine sponges. Many of them show a central 
perforation, like that in the spiculas of Spongilla.j: 
Other interesting forms occur in the infusorial strata of Virginia, but the limits of this paper 
will not allow me to present any more of them at present. I have transmitted specimens from 
* Ehrenberg refers tlie infusorial conglomerates of Oran, &c. to the chalk formation; but Rozet considered them as Urtiary 
deposits, and Prof. Rogers states that the beds discovered by him separate the miocene from the eocene tertiary beds of Virginia. 
t Since the above was in type, I have seen Ehrenberg’s figures of several species of Dictyocha in the Berlin Transactions, and 
find them to agree with the bodies above referred to. 
11 have reason to believe that similar siliceous spiculae occur in vast quantities in the external rays of some species of 
Actinia. 
