306 



AMERICAN TESTUDINATA. 



Part II. 



perishable their bodies are. The presence of well defined impressions of Medvisse 

 in the lithographic limestone of Solenhofen, specimens of which are preserved in 

 the Museum of Carlsruhe, confirms the assumption that they occur everywhere, 

 where Polypi and Echinoderms are found together. Among Mollusks, Acephala, 

 Gasteropoda, and Cephalopoda are always found in close association. Among 

 Articulata, this is also the case with Worms and Crustacea; Insects only appear 

 at a somewhat later jieriod. Whilst among Vertebrata, we find only Fishes, Selar 

 chians, and Ganoids in the lowest formations; next Amphibians, next Reptiles, 

 next Birds, and last. Mammalia. 



TABLE, 



SHOWING THE PERIOD OP THE FIRST APPEARANCE OF THE TESTUDINATA COMPARED WITH THAT OF THE 



OTHER ANIMALS. 



vy 



^ The most natural limit between the Cambrian zon at which animals and plants make their first 

 and Silurian periods seems to me to be the hori- appearance. 



The Table renders it unavoidable to refer notes 2, 3, 4, and 5 to the opposite page. 



