94 Sketch of the Infusoria of the family Bacillaria. 



the deposits of Oran, Zante, Caltasinetta, &c. (See Weaver's 

 View of Ehrenberg's Observations iu 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 discs which I believe 

 to belong to the genus Coscinodiscus. When perfect, the form 

 seems to be that of a torus, 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 

 directions, so that the curves present no inconsiderable resemblance 

 to those often seen on the back of watches ; at other times the 

 spots are found to form three sets of lines, making 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, Ya., but as I 

 have not seen Ehrenberg's account of the European species, I 

 cannot venture to name our own. 



Note, October 10th, 1841. — Since the above was ready for 

 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, Cos- 

 cinodiscus patina, and Gaillonella 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 be found as crowds of living creatures in the waters of 

 our seas. 



