Sketch of the Infusoria of the family Bacillaria. 93 



ing to the shores a ferruginous color in spaces even as much as a 

 hundred square yards in extent. 



7. Gaillondla ferruginea. Corpuscles very minute, convex on the 

 ends, ferruginous, oval, smooth, having the form of articulated threads, 

 often united, almost bi'anching, -yxyVii to xcrtrTr ii^^^. 



Ehrenberg states with a marli of doubt, that it occurs in all 

 ferruginous waters ; fossil in bog iron ore ; and in the yellow 

 opal of Bilin. A copy of Ehrenberg's figure may be seen in 

 Lyell's Elements of Geology, p. 39, (Am. Edit.) and in Pritch- 

 ard's Hist. Inf. fig. 129-130. I have often seen in bogs and 

 small streams, large quantities of a ferruginous colored floculent 

 matter which dispersed with great ease when touched, and in 

 which I have sometimes been able to see, by means of the micro- 

 scope, excessively minute filaments which were apparently mo- 

 niliform. I believe these filaments to be the G. ferruginea o( 

 Ehrenberg, v/hich is the same as the Oscillatoria ochracea of va- 

 rious algologists. The filaments are fragile and incombustible, 

 and are said to be composed of silicate of iron. (See Pritchard's 

 Hist. Inf p. 199 and 200.) 



ACTINOCYCLUS. 



Free, carapace simple, bivalve, (siliceous) form cylindrical, 

 (discoid) divided internally by several radiaiijig partitions ; spon- 

 taneous division imperfect in form of a chain. 



Ehrenberg mentions seven species, viz. A. ternarius, A. qua- 

 ternarius, A. qninarius, A. senarius, A. septenarius, A. octonarius, 

 and A. denarius, distinguished respectively by the number of 

 cells formed by the radiating partitions. Several species occur in 

 the " schiste of Oran" in Africa, in a formation which M. Rozet 

 considered as tertiary, but which Ehrenberg suspects is more 

 nearly connected with the chalk. 



It appears to me to be an interesting fact, that the remarkable 

 marine infusorial deposit discovered by Prof W. B. Rogers in 

 the tertiary formation of Virginia, appears to agree with the in- 

 fusorial conglomerate of Oran, in containing several species of 

 Actinocyclus, together with Gaillonella sulcata, and beautiful 

 punctate discs, which I suspect belong to the genus Coscinodis- 

 cus. I have seen no account of this last genus, but its name 

 appears peculiarly appropriate to the sieve-like discs which form 

 so large a portion of the infusorial stratum of Richmond, Ya. 

 Ehrenberg mentions Coscinodiscus patina as predominating in 



