DESCRIPTION OF GROUPS AND SPECIES. 43 



DESCRIPTION OF GROUPS AND SPECIES. 



Order TESTUDINES Batsch. Turtles and Tortoises. 



Reptiles with the body relatively short and broad. Quadrate bone immovably joined to the 

 pterygoid, the prootic, and paroccipital; its outer surface excavated to iorm a tympanic cavity. 

 Paroccipitals not consolidated with the exoccipital. Vomer single, if not missing. Pterygoids 

 closing the palate by their inner borders. Teeth never present; the jaws always armed with a 

 horny covering. Nasal opening single. Dorsal ribs each with a single head; at least the anterioi 

 ones intervertebrallv attacht. A nuchal bone always present. Cervical vertebrae eight; dorsals 

 ten. Epiplastra (clavicles) and at least six other bones present in the abdominal wall. No 

 sternum or sternal ribs ever developt. Each half of the pelvis composed of three bones, all con- 

 tributing to the acetabulum. Four limbs always present. Humeruswith ectepicondylar passage. 



This order of Reptilia is divided into two suborders, the Athkc.+: and the 

 Thecophora. 



Suborder ATHECjE Cope. 



Turtles which retain the primitive dermal armor, with at least traces of the subdermal 

 expansions connected with the ribs. 



Of this suborder there is no known representative from North American 

 deposits, unless possibly certain dermal bones that have been found to accompany 

 the remains of Basilosaurus (Zeuglodon) belonged to some otherwise unknown 

 species of the group. This is improbable, however, as shown by Dames (Pal. 

 Abhandl., v, 1894, p. 220). In Europe the suborder is represented by Eosphargis, 

 of the London Clay of England, by Psephophorus, of the Oligocene and Miocene of 

 the Continent, and perhaps by Pseudosphargis, of the Upper Oligocene of Germany. 

 The latter genus is based on a very imperfect skull; and, while presenting main 

 resemblances to Dermochelys, is not regarded by the present writer as being at all 

 certainly a member of the Atheca?. This turtle possest descending plates from the 

 parietals to the pterygoids. 



Suborder THECOPHORA Dollo. 



Turtles in which the primitive dermal armor has become obsolete or abolisht. Always a 

 more or less complete carapace formed by at least the expansions of the ribs, the nuchal bone 

 and with rare exceptions a series of neurals; usually a very complete shell formed by the bones 

 mentioned, together with series ot peripherals and a varying number ot plastral bones. Skull 

 always turnisht with descending parietal plates. 



This suborder, containing the vast majority of turtles, living and extinct, 

 consists of four superfamilies, the Amphichklydia, the Pleurodira, the Crypto- 

 dira, and the Trionychoidea. Of the first there are no living representatives. 



Key to Superfamilies of Thecophora. 



1. Mesoplastra present or absent. If absent, hinder lobe of plastron with rough scars for union with 

 pelvic bones except in Plesiochelyidae. 



a 1 . Mesoplastra always, so far as known, present; no plastral scars Amphichelydia 



a 2 . Mesolpastra present or absent; rough scars on hinder lobe of plastron Pleurodira 



x. Mesoplastra always absent; no sutural scars on plastron. 



j 1 . Peripheral bones always present Cryptodtra 



Peripheral bones present only in one genus now e.xisnng Trionychoidea 



a\ 



Superfamily AMPHICHELYDIA Lydekker. 



Thecophorous turtles having a carapace composed of neural, costal, and peripheral bones 

 and a plastron in which the epiplastra are in contact with the hyoplastra. Mesoplastra usually, 

 perhaps always, present. Intergular and inframarginai scutes probably always developt. 



