902 The American Naturalist. [November, 
gions. Of the former character are Svea, Phrynosoma, Barissia, 
Gerrhonatus, Hypsiglena and Salvadora ; of the latter kind, Spe- 
lerpes, Liolepisma, Osceola, Storeria and Systrurus. Characteristic 
of Medicolumbia generaly: Amblystoma, Rana, Sceloporus, 
Eumeces, Diadophis, Eutenia, Crotalus. Peculiar genera: 
Siredon, Hemigenius, 
Thorius, Epiglottophis, 
Malachylodes, Ogmius, 
Conopsis, Ophryacus. 
Neotropical genera: Oedipus, Anolis, Celestus, Atractus, Ninia, 
Drymobius, Bothriechis. 
(To be continued.) 
FOSSILS AND FOSSILIZATION. 
By L. P. GRATACAP. 
L 
A fossil, in Paleontology, is any indication of life which has 
become entirely or partially altered in its substance or condi- 
tion by the mineral or chemical agencies of its environment. 
As an “indication ” it embraces the widest possible series of 
remains which have, or could have, any connection with liv- 
ing organisms, from the bones of a vertebrate, the hard parts of 
an invertebrate, the foliage, fronds, seeds and wood of plants, 
to the fillings of worm burrows, the tracks of insects, reptiles, 
mammals, mollusca and crustaceans, and those problematic 
impressions which have been referred to Medusa, or those by 
Prof. Hall to the soft parts of an Orthoceras. And it also in- 
cludes the stony casts formed by the entrance of extraneous 
mud or silt, sand or chemical deposits within the hard parts of 
animals upon their death and the disappearance of the soft 
-parts by decay. The hard parts, upon removal by solution, 
leave the impressions of their interior upon this soft filling 
“which faithfully copies the contour and size of the organism. 
