94 Sketch of the Infusoria of the family Bacillaria. 
the deposits of Oran, Zante, Caltasinetta, &c. (See Weaver's 
View of Ehrenberg’s Observations in Lond. and Ed. Phil. Journ. 
for May, 1841, p. 393.) In figs. 9, 10, and 11, are represented sev- 
eral fossil species of Actinocyclus from Richmond, Va. ; the same 
species also occur fossil in cliffs on the Rappahannock River. In 
figs. 12, 13, and 14, are represented the dises which I believe 
to bélong to the genus Coscinodiscus. When perfect, the form 
seems to be that of a tortis, having the circular bases covered with 
hexagonal or circular spots, which present considerable variety 
in their size and arrangement in different specimens. The most 
usual disposition of the spots is in rows corresponding with the 
radii, as shown in the large specimen fig. 14. In consequence of 
this arrangement, they also form beautiful spiral rows in other 
1s, So that the curves present noi 
#8 tides often seen on the back of watches; at other times the 
spots are found to form three sets of lines, foakeinig angles of 60° 
and 120° with each other, as shown in fig. 12, and on others the 
spots are disposed without ‘much apparent regularity, frequently 
having a star-like figure in the centre. ‘The spots are so small 
on some of the discs, as to be almost invisible even by the high- 
est magnifying powers; on others, as in fig. 14, they are quite 
large and distinctly hexagonal. The largest discs have not al- 
ways the largest spots. There are certainly several species of 
this genus in the infusorial stratum of Richmond, Va., but as 
have not seen Ehrenberg’s account of the European ee I 
cannot venture to name our own. 
Note, October 10th, 1841.—Since the above was ready ie 
the press, I have seen in the appendix to Pritchard’s History of 
Infusoria, living and fossil, some interesting statements of recent 
discoveries by Ehrenberg, with reference to the genera of Acti- 
nocyclus and Coscinodiscus. It appears that these genera, which 
were first discovered in a fossil state in the schiste of Oran, Cal- 
tasinetta, Zante, &c., have also been recently found in sea water, 
and that many of the living species are identical with the fossil 
ones ; indeed, Ehrenberg states that Actinocyclus senarius, C’os- 
cinodiscus patina, and G‘aillonella sulcata, species now living, 
may be shown as the chief forms met with in the chalk marls 
of Sicily, and also that the species of the chalk formations are 
yet to bees cols — creatures in the waters of 
our seas. naa: 
