Co-existence uf Saurian and Molluscous Forms. 129 



found. When we consider all the conditions under which the re- 

 mains of plants may be accumulated, and the difficulty often of de- 

 terminino- the real character of the plants themselves, it would ap- 

 pear desirable to obtain more information respecting the distribution 

 of fossil plants at different geological times than we now possess, 

 before we conclude that we have evidence enough to speak of the 

 characteristic plants of different geological epochs with the confidence 

 sometimes used. It would appear very desirable, under present in- 

 formation, to regard the subject more locally, and always with refer- 

 ence to the probable physical conditions under which the plants may 

 have been entombed. 



4. Co-existence of certain Saurian and Molluscous Forms at 

 Equal Geological Times. — To Professor Owen we are indebted for 

 a description of saurian remains discovered by Professor Henry 

 Rogers in a greensand deposit of the United States, considered re- 

 ferable to the age of part of the cretaceous accumulations of Europe. 

 The specimens placed befoie Professor Owen enabled him to add 

 some facts to the osteology of the Mosasaurus, and to discover some 

 species of saurians, especially of the procoelian form of crocodile, not 

 previously known in strata older than the tertiary deposits termed 

 eocene. After very important osteological details respecting the 

 Mosasaurus, which require to be studied in the memoir itself, in order 

 fully to appreciate the labours of our colleague upon this subject, he 

 states, that, considering certain of the bones to belong to the Mosa- 

 saurus, " they indicate the extremities of that great saurian to have 

 been organised according to the type of the existing Lacertia, and 

 not of the Enaliosauria or marine lizards ;" and adds, " two species, 

 at least, of true Lacertia have left their remains in our English 

 chalk." 



Professor Owen next notices some remains of a pro'oelian reptile, 

 and proposes to indicate the saurian and probably mosasauroid 

 genus to which it belongs by the name of Macrosaurus. Upon 

 other remains he establishes the genus Hyposaurus. an Amphicoelian 

 crocodile, and then notices specimens from the same localities laid 

 before him by Professor Henry Rogers, which he remarks are " the 

 first evidences of the genus of the modern Crocodilus or Alligator 

 that have been discovered in sti-ata older than the eocene tertiary." 



The accumulations amid which these saurians have been detected 

 are inferred, from the marine remains found in them, to be of the 

 same age as part of the cretaceous series of Western Europe, simi- 

 lar marine molluscs having been considered to exist and to have been 

 entombed in mineral matter at the same geological period in the 

 seas surrounding the shores of land iu the areas now occupied by 

 the United States and Western Europe. The remains des(-ribed by 

 Professor Owen thus possess not only high interest, as additions to the 

 forms of life which have existed at different times on our earth, but 



VOIi. .\LVII. NO. XOIII.— .lULV 1849. I 



