Sentence:  [I]n fresh water we find some of the most anomalous forms now known in the world, as the Ornithorhynchus and Lepidosiren, which, like fossils, connect to a certain extent orders now widely separated in the natural scale. These anomalous forms may almost be called <WSD>living fossils</WSD>; they have endured to the present day, from having inhabited a confined area, and from having thus been exposed to less severe competition. 
Meaning of the word marked with <WSD> tags:  Any species discovered first as a fossil and believed extinct, but which is later found living; an organism that has remained unchanged over geological periods. (from 1859)