330 Sketch of the Infusoria of the family Bacillaria. 



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, (fee* 



PL 3, fig. 25, shows a sihceous ring with projecting spines ; it 

 is possibly a fragment of the preceding. 



PI. 3, fig. 26, shows a circular ring connected with a concentric 

 hexagon by six rays proceeding from the angles of the hexagon. 

 The spaces within the hexagon and below the rays are perforations. 

 It is possibly another species of Dictyocha. It occurs occasionally 

 among fossil infusoria from Richmond and Rappahannock cliffs. 



PI. 3, 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 perfo- 

 rated by similar holes. Of the nature of these curious fossils, I 

 am entirely ignorant. They occur with the preceding. 



PI. 3, fig. 29, shows a triangular binary siliceous body, resem- 

 bling some of the fluviatile species of Euastrum. The surface is 

 covered with minute dots, some of which form lines leading 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 PI. 3, figs. 30 to 35 show siliceous bodies which are quite 

 abundant with the preceding forms, and which I suspect are spi- 

 cules of marine sponges. Many of them show a central perfora- 

 tion, like that in the spiculaB of Spongilla.f 



Other interesting forms occur in the infusorial strata of Vir- 

 ginia, but the limits of this paper will not allow me to present 

 any more of them at present. I have transmitted specimens from 

 Richmond to Ehrenberg, and he will doubtless determine to what 

 extent the African and American beds agree in their microscopic 

 fossils. As the infusorial strata of Virginia belong decidedly to 

 the tertiary epoch, and yet appear to agree remarkably with what 

 Ehrenberg considers as chalk marl from Oran, a revision of the 

 evidence upon which the siliceous infusorial conglomerates of 

 Africa and the south of Europe were referred to the cretaceous 



* Since the above was in type, I have seen Ehrenberg's figures of several spe- 

 cies of Dictyocha in the Berlin Transactions, and find them to agree with the 

 bodies above referred to. 



t I have reason to believe that similar siliceous spiculae occur in vast quantities 

 in the external rays of some species of Actinia. 



