670 SCIENCE PROGRESS 



of the Simbirsk district ; while a new ichthyosaur from the 

 North German Chalk is described by Dr. A. Broili in vol. lv. 

 pp. 295-302 of the Palceontographica with special reference to 

 the " hypophysenloch " in the group generally. 



From ichthyosaurs to mosasaurs is an easy transition and 

 reference may therefore be made in this place to a paper on 

 remains of the latter group from the Supra-Cretaceous beds of 

 Orenburg contributed by Mr. N. Bogolutow to vol. xii. of 

 Ann. Ge'ol. et Min. de la Russie, in which a new Liodon is 

 described. 



Turtles and tortoises have formed the subject of several 

 papers published during the year, among which special interest 

 attaches to one by Mr. G. R. Wieland, published in the American 

 Journal of Science, vol. xxvii., on the gigantic American Cre- 

 taceous turtles Archelon and Protostega. Apparently in 

 conformity with the needs of a pelagic existence, the carapace 

 in these turtles has been lightened by a great reduction in 

 the size of the costal plates ; this reduction being carried to the 

 greatest extent in Archelon, where the absorption has also 

 extended to the neural bones, many of which seem to have 

 been diminished to mere films. Upon these aborted neurals 

 is, however, imposed a series of digitated epineural dermal 

 ossifications, undoubtedly corresponding to the neural keel 

 of the living leathery turtle {Dermochelys) and discharging the 

 function of the aborted neurals. Archelon seems, indeed, to 

 have been covered with a continuous leathery skin and to have 

 carried a series of dorsal keels comparable with those of 

 Dermochelys. It is thus evident that Archelon shows a marked 

 tendency to do away with the bony plates of the upper shell and 

 to replace them with a superficial series of smaller bones com- 

 parable to the mosaic-like carapace of the leathery turtle. 



In this respect the structure of Archelon and the allied 

 contemporary genus has a most important bearing on the 

 phylogeny of the turtles and, indeed, of the chelonian order 

 generally. For the leathery turtle is referred by many 

 naturalists to a group (the Atheca or Athecata) totally distinct 

 from the one including all other chelonians. But if, as the 

 American Cretaceous forms appear to indicate, the carapace of 

 the leathery turtle is a secondary structure originally super- 

 imposed on the vanishing carapace of a turtle of a more or less 

 ordinary type, the essential distinction between Athecata and 



