58 FOSSIL TURTLES OF NORTH AMERICA. 



characters the skull appears to be cryptodiran in structure. The neck must be regarded as 

 primitive and intermediate between the Cryptodira and the Pleurodira. No features strictly 

 pleurodiran appear. 



The cervical vertebrae are described under the species Baena riparia and Chisternon 

 hebraicum. Considering the shortness of the neck, the structure of the vertebrae, and the nar- 

 rowness of the anterior border of the carapace, it seems probable that these turtles were able to 

 find in the shell little protection for their heads. 



The tail was long, resembling that of Chelydra. With two or three of the skeletons there 

 have been found some conical bones, the bases of which were buried in the skin. Some of 

 these are symmetrical and it appears probable that they were placed in a row on the upper 

 midline of the tail, as in Chelydra. Others of these bones are unsymmetrical, and possibly 

 formed parts of lateral rows on the tail. If there had been an armor of dermal bones on the 

 legs it would probably have been observed in some of the specimens. 



For the shoulder-girdle and the pelvis the reader is referred to succeeding descriptions of 

 Baena and Chisternon. The limbs are of the walking type. 



The following key may be of some use in determining the genera of the family: 



A. No interhumeral scute. 

 a. A preneural present. 



b. No supramarginal scutes Chisternon 



bb. Supramarginals present Boremys 



aa. No preneural so far as known. 



c. Plastron projecting little, if at all, beyond front of carapace. 



d. Skull with choarue well in front Baena 



dd. Skull with choanae between orbits Eubaena 



ddd. Skull unknown. Plastron with median fontanel Probaena 



cc. Front of plastron projecting in front of the excavated carapace. 



e. The axillary and inguinal buttresses not greatly developt Thescelus 



ee. Axillary buttresses rising high on first costals Charitemys 



aaa. Characters not well known. A suprapygal present; the vertebral scutes broad; 9 pairs 



of costals in type Neurankylus 



AA. Plastron with an interhumeral scute. 



a. Outer surface of plastron rugose Polythorax 



aa. Outer surface of plastron with globular elevations Naomichelys 



Genus PROBAENA Hay. 



A genus closely related to Baena, but with a more deprest carapace, the hinder border of 

 which is little or not at all notcht. Vertebral scutes broader than the costal scutes. Plastron 

 with its hinder lobe rounded. A fontanel (permanent ?) between inner ends of mesoplastra. 



It is not improbable that when the skull and the cervical vertebras of this genus shall be 

 discovered, it will prove that it belongs to the Pleurosternidae and that the Baenidae had not yet 

 diverged from the former family. 



Probaena sculpta Hay. 



Plate 7, fig. 5. 

 Probaena sculpta, HAY, Ann. Carnegie Museum, II, 1903, p. 201, plate iii, figs. I, 2. 



The type is a small and somewhat imperfect turtle, represented by about three-fourths of 

 the carapace and the greater portion of the plastron. 



It belongs to the Carnegie Museum, Pittsburg, and was collected by Prof. J. B. Hatcher, 

 in 1901, in the "Marsh quarry" in the lower portion of the Morrison, or Atlantosaurus beds, 

 8 miles north of Canyon City, Colorado. The catalog number is 917. 



The length of the carapace is at present 105 mm., very near the original length; the 

 width is 70 mm. The shell has apparently been rather flat, but probably somewhat less so in 

 life than at present. The greatest distance between the upper and the lower surfaces is now 27 

 mm. The borders of the carapace behind the inguinal notches are considerably flared upward, 

 but this may be due somewhat to post-mortem distortion. This border appears to have been 



