8 4 



FOSSIL TURTLES OF NORTH AMERICA. 



is larger than that of the other species, the horizontal diameter being 24 mm. The perpen- 

 dicular diameter is now only 16 mm., but this is due, no doubt, to crushing. From the orbit to 

 the tympanic cavity is 22 mm. 



The roofing of the temporal region resembles that of E. cephalica. Few of the sutures of 

 the upper side of the skull can be traced with certainty; but it is evident that the parietal 

 union with the squamosal had been severed by the excavation in the hinder border of the roof. 

 There are reasons for believing that the parietals were each 15 mm. wide posteriorly. If the 

 prefronto-nasal suture is where it seems to be, the nasals were unusually large, running along 

 the midline 8 mm. The parieto-frontal and the fronto-prefrontal sutures can not be deter- 

 mined with certainty. The nasal opening has now a width of 23 mm. One premaxilla is 

 present and has the height and the width each 9 mm. The maxilla, below the orbit, is 1 1 mm. 

 wide, being thus narrower than that of E. cephalica. 



The upper surface of the skull is rough with narrow ridges, separated by sharp furrows. 

 This interferes with the tracing of the sutures; for the latter do not appear to be really absent. 

 Occasional narrow grooves indicate that the skull was covered with horny plates; but these 

 can not be mapt. 



FIGS. 69 AND 70. Eubaena latifrons. Skull of type. Xf . 

 69. Skull seen from above. 70. Skull seen from below, fmx, premaxilla; vo, vomer. 



The base of the skull and the roof of the mouth resemble in general the same regions of 

 E. cephalica. At the pterygoid constriction the width is only 16 mm. The postpalatine 

 foramina are placed 24 mm. apart; whereas, in E. cephalica they are only 18 mm. apart. The 

 maxillary triturating surfaces appear not to have been so wide as those of E. cephalica. As in 

 the latter species, they are bounded on the inner margin by a rough ridge. 



Genus CHISTERNON Leidy. 



Related closely to Baena, but having 2 bones, an anterior and a posterior, occupying the 

 region of the nuchal of Baena. Normally 2 scutes occupying the area corresponding to the first 

 vertebral of Baena. No supramarginals. Maxilla with a nearly plane triturating surface. 



Type, Baena undata Leidy. 



The genus was based by Dr. Leidy on the presence of the mesoplastra, but these were after- 

 wards found to be present in Baena arenosa also. The existence of the two bones in the region 

 of the nuchal, with the absence of supramarginals, will characterize the genus. 



Two specimens of C. undatum and one belonging to Cope's Baena hebraica in the American 

 Museum of Natural History show unmistakably the two bones mentioned as occurring in the 

 region of the anterior neural. 



Remarks on the significance of the preneural and the supernumerary scutes will be found 

 on page 57. 



