Sketch of the Infusoria of the family Bacillaria. 329 



whose list of the species is given in this Journal, Vol. xxxix, p. 

 193 ; Blue Hill Pond, and various other localities in Maine, 

 discovered by Dr. Jackson ; Manchester, Spencer, Wrentham, 

 Bridgewater, Andover, &c. in Massachusetts, discovered by Prof. 

 Hitchcock, and Smithfield and other places in Rhode Island, dis- 

 covered by Owen Mason, Esq. The largest and most conspicu- 

 ous species from all these localities are Navicula viridis, PL 2, 



fig. 16, Navicula ? PI. 2, fig. 23, Cocconema , PI. 3, 



fig. 11, Eunotia arcus, PI. 2, fig. 26. With these occur various 

 smaller species, and numerous siliceous spicules of fresh-water 

 sponge, PI. 3, fig. 18, a to d, and other siliceous bodies of organic 

 origin, such as the Amphidiscus rotula of Ehrenberg, PI. 3, fig. 

 20, and others whose nature is unknown, but which I suspect to 

 be of vegetable origin, perhaps prickles of aquatic grasses. See 

 PI. 3, figs. 21, 22 and 23. 



The most interesting American deposit of fossil infusoria, is the 

 " infusorial stratum" discovered by Prof W. B. Rogers, of the 

 University of Virginia. It is peculiarly interesting 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 with those of Oran 

 in Africa. This is shown by the occurrence of vast quantities of 

 various species of Coscinodiscus and Actinocyclus, with Gaillo- 

 nella sulcata ? &c. Believing that it will be of great interest to 

 geologists both at home and abroad to trace out this correspond- 

 ence 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 3d, a number of figures of siliceous bodies not before de- 

 scribed, found in the infusorial stratum of Virginia. The fol- 

 lowing is a brief account of these bodies. 



In PI. 3, fig. 24, a, b, c, are shown difierent 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 



* Ehrenberg refers the infusorial conglomerates of Oran, &c. to the chalk for- 

 mation, but Rozet considered them as tertiary deposits, and Prof. E.ogers states 

 that the beds discovered by him separate the miocene from the eocene tertiary beds 

 of Virginia. 



Vol. XLiii, No. 2.— July-Sept. 1842. 42 



