163 SKETCH OF THE INFUSORIA 



organic origin, such as the Amphidiscns rotula of Ehrenberg, PL 

 111, lig. :20, and olhcrs whose nature is unknown, but which I sus- 

 pect to be of vegetable origin, perhaps prickles of aquatic grasses. 

 See PI. Ill, 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 infu- 

 soria 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. Tliis is show^n by the occurence of vast quantities of 

 various species of Coscinodiscus and Actinocyclus, with Gaillo- 

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

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

 dence 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 described, 

 found in the infusorial stratum of Vu'ginia. The following is a 

 brief account of these bodies. 



In PI. Ill, 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. I 

 suspect that these belong to the genus Dictyocha of Ehrenberg, 

 several species of which occur at Oran, Caltasinetta, (kc.f 



PI. Ill, fig. 25, shows a siliceous ring witli projecting spines ; 

 it is possibly a fragment of the preceding. 



* Ehrenberg refers the infusorial conglomerates of Oran, 6cc., to the chaiA: formation, 

 but Rozet considered them as tertiary 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 Elirenberg's figures of several species of 

 Dictyocha in the Berlin Transactions, and find them to agree with the bodies above re- 

 ferred to. 



