500 



PHYSICAL GEOGRAPHY. 



Description of Plates. 



All of the figures, with the exception- of 23 and 24, are magnified five hundred 

 diameters, or two hundred and fifty thousand times superficial. Fig. 23 is magnified 

 about three hundred diameters, and Fig. 24 one hundred diameters. All of the 

 figures, with the exception of the two mentioned, are exact portraits of specimens in 

 the collection of the author, and are intended to be as perfect delineations of the 

 diatoms represented as could be obtained, as the drawings have been made with 

 special care to that end. This fact is mentioned, as most of the plates of diatoms 

 published do not give correct ideas of these organisms, and are usually drawn or 

 engraved by persons not possessed of an intimate acquaintance with the objects 

 intended to be represented. The plates have been obtained by photography direct 

 from the author's drawings, without the intervention of any engraver, and are, there- 

 fore, truthful reproductions of them. 



Plate I. 



Fig. I. Front view of Triceratium Montereyii. From the marine fossil "infusorial 

 stratum," of Monterey, Cal. This figure shows the connecting membrane, which 

 is difierently sculptured from the valves. 



Fig. 2. Front view of Triceratium punctatum. In this specimen no connecting mem- 

 brane has been developed. From the harbor of Charleston, S. C. 



Fig. 3. Side view showing the valve of Pinnularia nobilis. From Germany. 



Fig. 4. Front view of Rhabdonema arcuatum. From the harbor of Salem, Mass. 



Fig. 5. Side view of Pleurosigma angiilata. From the coast of France. 



Fig. 6. Side view of Pleurosigma fasciola. From the harbor of New Haven, Conn. 



Fig. 7. Side view of Triceratium punctatum. From Charleston, S. C. 



Fig. 8. Side view of Pleurosigma Balticum. From the coast of England. 



Fig. 9. Side view of Pleurosigma quadratum. From the coast of England. 



Fig. 10. S\di&yie.v/ oi Coscinodiscus radiatus. From the marine fossil stratum of Oran, 

 Algiers. In this specimen, as is very commonly the case, the radiant arrange- 

 ment of the markings is obscure. 



Fig. II. SiA& Vi&w oi JVavicula didyma. From the coast of France. 



Fig. 12. Side view of Triceratium favus. From the harbor of Charleston, S. C. 



Plate II. 



Fig. 13. A specimen showing both front and side views of Gomphonema constrictum, 

 as well as the arrangement of the stipes or stalk. From Marion, N. J. 



Fig. 14. Front view of Achnanthes brevipes, showing the flag-like appearance of the 

 perfect individual when attached to some submerged substance by means of its 

 stipes. From the coast of England. 



