1910.] The Cctacea. 411 



(5) The confusing web of cross resemblances, e. cj., of I>itopterns to 

 Perissodactyls, of Hyracoids to Protypotheres and Perissodactyls has been 

 conditioned by the facts: (a) that the several orders have been derived 

 from related families of protungidates having a similar "potential of evolu- 

 tion"; (6) that these protungulate families inherited in common a great 

 number of primitive Placental characters which they distributed in various 

 combinations to their several lines of descendants; (c) that many of the 

 characters which have been used to unite very different groups {e. g., the 

 interlocking carpus of Artiodactyls and Perissodactyls) were at first less 

 defined and more plastic but later became fLxed ordinal characters. 



CHAPTER X. GENETIC RELATIONS OF THE CETACEA. 



Historical Notes. 



A. On the Zeuglodontia. 



1670. Agostino Scilla describes and figures a fossil tooth of the animal 

 later known as Zeuglodon. Scilla's figure is reproduced in de Blainville's 

 ' Osteographie ' (tom. ii, "Phoca."). 



1834. Harlan applies the term " Basilosaurus" to certain fragmentary 

 vertebrae belonging to the genus now commonly known as Zeuglodon. 



1836. Agassiz examines Scilla's fragment and in his 'Poissons fossiles' 

 refers to it as "une espece remarquable du genre Phoca qui differe sensible- 

 ment de tons nos Phoques vivans." He later calls it Phocodon (Palmer, 

 1904). 



1839. Owen having determined the mammalian nature of "Basilo- 

 saurus" proposes to substitute the name Zeuglodon. 



1840. Grateloup describes certain remains as " Squalodon," supposing 

 them to be saurian in nature (Palmer). H. von Meyer refers these remains 

 to the Cetacea. 



1840. De Blainville refers Scilla's original fragment to the Pinnipedia 

 and distinguishes it from Squalodon, since in Scilla's specimen the teeth had 

 two roots, in Squalodon only one. De Blainville calls it "Phoca melitensis 

 antiqua." 



1849. J. Midler monographs the group, which he considers Cetacean 

 in the broad sense, intermediate between the Pinnipedia and the Cetacea 

 proper, but occupying an order by itself. 



1872. Gill applies the term "Zeuglodontia" to a suborder of the order 

 "Cete." 



