16 



types; the genus Gaviab's having one Eocene species, and the 

 Alligator being represented only in the latest deposits. 



It is worthy of special mention in this connection, that no 

 true Lacertilia, or Lizards, and no Ophidia, or Serpents, have 

 yet been' detected in American Cretaceous beds; although their 

 remains, if present, would hardly have escaped observation in 

 the regions explored. The former will doubtless be found, as 

 several species occur in the Mesozoic of Europe ; and perhaps 

 the latter, although the Ophidians are apparently a more mod- 

 ern type, (in the Eocene lake-basins of Western America, re- 

 mains of Lizards are very numerous, and indicate species much 

 larger than any existing to-day. Some of these, the Olyplosau- 

 ridce, were protected by a highly ornamented bony coat of mail, 

 and others were covered with scales, like recent Lizards. A 

 few resembled, in their more important characters, the modern 

 Iguana. The genera best represented in the Eocene, are, Olyp- 

 tosaurus. Iguanavus, Oreosaurus, Thinosaurus, Tinosaurus and 

 Saniva. i Some of these genera appear to have continued into the 

 Miocene, but here, as well as in the Pliocene, few remains of 

 this group have been found. It is not improbable that some 

 of our extinct Eeptiles may prove to belong to Rynchocephala, 

 but at present this is uncertain. The genus Notosaurus, from 

 Brazil, has biconcave vertebras, and some other characters 

 which point to that group. No Dicynodonts or Thecodonts 

 have as yet been found in this country. 



The first American Serpents, so far as now known, appear 

 in the Eocene, which contains also the oldest European species. 

 On the Atlantic border, the genus Titqnophis (Dinophis) is 

 represented by several species of large size, one at least thirty 

 feet in length, and all doubtless inhabitants of the sea. In the 

 fresh-water Western Eocene, remains of snakes are abundant, 

 but all are of moderate size. The largest of these were related 

 to the modern Boa Constrictors. The genera described are 

 Boavus, Lithophis and Limnophis. The Miocene and Pliocene 

 Snakes from the same region are known only from a few frag- 

 mentary remains. 



