OF THE FAMILY BACILLARIA. 163 



PI. Ill, fig. 26, shows a circular ring connected with a concen- 

 tric hexagon by six rays proceeding from the angles of the hexa- 

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

 perforations. It is possibly another species of Dictyocha. It oc- 

 curs occasionally among fossil infusoria from Richmond and 

 Rappahannock cliffs. 



PI. Ill, fig. 27, shows a curious fragment, apparently siliceous, 

 having a campanulate form wdth a projection at the apex, and 

 pierced with large holes. Fig. 28 shows an ovoid body perfor- 

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

 am entn-ely ignorant. They occm- with the preceding. 



PI. Ill, fig. 29, shows a triangular binary siliceous body, re- 

 sembling some of the fluviatile species of Euastrum. The surface 

 is covered with minute dots, some of which form fines leading 

 from the centre to the angles. Perhaps this belongs to Ehren- 

 berg's genus Tnceratium, of" which species occiur fossil at Oran, 

 and living in Cuxhaven. 



In PI, III. figs. 30 to 35 show sificeous bodies which are quite 

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

 cuIeb of marine sponges. Many of them show a central perfor- 

 afion, like that in the spiculsB of Spon^illaJ^ 



Other interesting forms occur in the infusorial sfrata 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 then: 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 

 group, appears necessary. Should the true age of either the Ameri- 

 can or African deposits be determined by means of the fossil in- 

 fusoria, it will be an additional instance of the importance of this 



* I have reason to believe that similar siliceous spiculse occur in vast quantities in the 

 external rays of some species of Actinia. 



