CLASSIFICATION. 25 



THE CLASSIFICATION OF THE TURTLES. 



It is not the purpose of the writer to give here an account of the various schemes 

 of classification that have been proposed by writers on the turtles. For such an 

 account the reader may consult the third part of the sixth volume of Bronn's 

 Klassen und Ordnungen des Thierreichs, beginning with page 347. The following 

 is the arrangement of suborders, supertamihes, and families accepted by the writer. 



All of these families, except those in italics, have fossil representatives. 



Order Testudines. 

 Suborder I. Athecae. 



Family. Dermochelyidae. 

 Suborder II. Thecophora. 



Superfamily I. Ampliiclielydia. 



Families, Pleurosternida?, Baenidie, Plesiochelyidae ? 

 Superfamily 2. Pleurodira. 



Families. Bothremyidae, Pelomedusidae, Chelyidae, Miolanidae. 

 Superfamily 3. Cryptodira. 



Families. Thalassemydidae, Toxochelyidae, Desmatochelyida?, Protostegidae, Cheloniida?, 

 Tretosternidas, Chelydridae, Dermatemydida?, Platysternidce, Kinosternidte 

 Carettoclielydae, Emydidae, Testudinida?. 

 Superfamily 4. Trionychoidea. 



Families. Plastomenida;, Trionychidae. 



The arrangement and names of the suborders and superfamilies above given 

 are the same as those used by Mr. George A. Boulenger in his Catalogue of the 

 Chelonia of the British Museum, 1889. Mr. Richard Lydekker employs practically 

 the same groups in his Catalogue of the Fossil Reptilia of the British Museum, 

 part in, 1889; but to some of his groups are given different names. Dr. Louis 

 Dollo, of Brussels, also divides the turtles into the two suborders Atheca; and 

 Thecophora. Altho this eminent writer believes that Dermochelys, the only living 

 representative of the Athecae, was derived from the Cheloniida?, he separates it as 

 the representative of a distinct suborder on account of its extreme modifications of 

 structure. It was Cope who first proposed to make this turtle the type of a distinct 

 suborder. 



In his Bibliography and Catalogue of the Fossil Vertebrata of North America, 

 1902, the present writer assigned to the Trionychoidea, under the name Trionychia, 

 the rank of a suborder. A further consideration of the subject has convinct him 

 that these turtles should rank lower than a suborder; not higher than a super- 

 family. Indeed, they appear to have brancht oft from the earliest Cryptodira; 

 but their lineage is so ancient, and they have undergone so many modifications of 

 structure, that they are of equal rank with the Cryptodira. The skull is more like 

 that of the Cryptodires than that of the Pleurodires, but has developt peculiarities 

 of its own. Like the Cryptodires, the temporal roof has never been eaten away from 

 below, and always a zygomatic arch remains. The neck is wholly cryptodiran in 

 its modifications and is retracted within the shell in the same way. This is a feature 

 unique among animals, and it seems improbable that it could be hit upon independ- 

 ently by two distinct groups of turtles. The pelvis in its parts and its relationships 

 to the shell is entirely cryptodiran. 



Ernst Haeckel, in his Systematische Phylogenie der Wirbelthiere, 1895, page 326, 

 has taken the position that the Trionychoidea had probably arisen already in the 

 Triassic and that they are to be lookt upon as the group from which all the The- 

 cophora have been derived. That the group was establisht even in the Trias is 

 possible; that it gave origin to the other groups of Thecophora seems quite impos- 



