"The vast deposits of fluviatile shells which exist in Florida, at Picolata, Volusia, and Enterprize are of great geological interest. The two latter places present bluffs and hills of from forty to fifty feet in height, extending half a mile or more from the river, that are composed of scarcely anything but well-preserved shells of _Paludina vivipara_, _Ampullaria depressa_, some undetermined species of _Unio_, _Helix septemvolvis_, _Melania_, and a few others. There is but a scanty mixture of earth, and the shells are clean, and look as if they had been washed ashore after the death of their inhabitants. In some places the beds are sandy, and are hardening into a calcareous shelly sandstone. In one such bed the superficial stratum furnished a few bones of turtles and undetermined fragments, the bones of some large vertebrate animal. This is, I believe, the locality where Count Pourtalés collected human bones in a recent sandstone.... No microscopical forms were detected in these beds after the most careful search."[352] [352] Dr. J, W. Bailey, in Smithsonian Contributions, vol. ii. Article viii. p. 23. [Illustration: Lign. 125. Terebratula and Rhynchonella; _nat._ _Chalk. Lewes._ Fig. 1.--Rhynchonella plicatilis. 1_a_.--The same species, partly open. 2.--Rhynchonella subplicata. 2_a_.--Front view of the same. 3.--Terebratula semiglobosa; side view. 3_a_.--The same species, seen from above. 4.--Terebratula subrotunda. ] Fossil Shells of the Brachiopodous Mollusca.--These are bivalve shells, of which nearly five hundred species are found in the British strata. They occur in incredible numbers in the ancient rocks, to which several genera are restricted; while some continue through all the formations, and inhabit the present seas; but the existing genera are few. [Sidenote: TEREBRATULA.] Terebratula (_bored, alluding to the perforated beak_), _Lign. 125._--The common species of this genus must be familiar to all who have ever looked into a quarry of Chalk, or of Shanklin sand, in the south-east of England. They have been humorously called the _Fossil Aristocracy_, from the incalculable antiquity of their lineage.