I 



24 



MICROSCOPICAL OBSERVATIONS. 



from the river, which are literally composed of almost nothing else but well 

 preserved shells of the Paludina vivipara. Say, Ampullaria depressa, Say, some 

 undetermined species of Unio, Helix septemvolvis, Melania, and a few others. 

 There is scarcely any mixtvire of earth, but the shells are clean, and look as if 

 they had been washed ashore after the death of the animals. In some places 

 the beds are sandy, and are hardening into a calcareous 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 

 same locality where Covmt Pourtales collected human bones in a recent sandstone. 

 That the sandstone is recent I have no doubt, but the shells from which these 

 banks are formed, though belonging to species now inhabiting the lake and 

 river, were probably accumulated thousands of years ago, under very different 

 circumstances as to elevation, topography, &c., from those now existing. They 

 certainly form the most remarkable fresh-water deposits in the United States. 

 No microscopical forms were detected in these beds, after the most careful 

 search . 



PONDS NEAR ENTERPRISE, FA. 



April \2th to ISth, 1^50. — In fresh-water ponds, near Mr. Duval's boarding 

 house at Enterprise, I found a most abundant supplyof interesting microscopica;l 

 forms, among which the following were identified : 



Desmidie^. 



Ankistrodesmus falcatus, Corda. 

 Aptogonum Baileyi, Ralfs. 



" desmidium, Ehr. 



*Cosmarium depressum, B. PI. 1, fig. 1. 



" pyramidatum, Breb. 



Closterium lunula, Ehr. 



" setaceum, Ehr. 

 Didymocladon furcigerus, Ralfs. 



* " Cerberus, B. PI. 1, figs. 15, 16. 



* " longispiiium, B. PI. 1, fig. 17. 

 Didymoprium Grevilhi, Ralfs. 



" Borreri, Ralfs. 



*Docldium hirsutum, B. PI. 1, fig. 8. 



" minutum, Ralfs. PL 1, fig. 3. 



undulatiun, B. PI. 1, fig. 2. 

 Euastrum ampullaceum, Ralfs. 



" elegans, Breb. 



" insigne, Hass. 



" rostratum, Ralfs. 



" sublobatum, Breb. 



" verrucosum, Ehr. 



Hyalotheca dissiliens, Breb. 

 Micrasterias Baileyi, Ralfs. 



* " arcuata, B. PI. 1, fig. 6. 

 " denticulata, Breb. 



* Micrasterias expansa, B. PI. 1, fig. 7. 



" fimbriata, Ralfs. 



" pinnatifida, Kg. 



* " quadrata, B. PI. 1, fig. 5. 



" rotata, Ralfs. 



" truncata, Breb. PI. 1, fig. 20. 



Penium Jenneri, Ralfs. 



" margaritaceum, Breb. 

 Sphaerozosma excavatum, Ralfs. 



" serratum, B. 



" pulchrum, B. 



Spirotaenia condensata, Breb. 

 Staurastrum aristiferum, Ralfs. 



" gracile, Ralfs. 



" margaritaceum, Ehr. 



" tricorne, Breb. 



Triploceras verticillatum, Breb. PI. 1, fig. 



gracile, B. PL 1, fig. 10. 

 Tetmemorus Brebissonii, Ralfs. 

 Xanthidium armatum, Breb. 



" fasciculatum, Ehr. . 



" octocorne, Ralfs. 



*Aporea ambigua, B. PL 3, fig. 3. 



