0. P. Hay— Fossil Turtles in the Marsh Collection. 263 



This species differs from B. hatcheri in the greater thick- 

 ness of. the bones of the carapace and in the shorter lobes of 

 the plastron. It is named in honor of the late Professor 

 Othniel C. Marsh. 



Ba'ena cephalica sp. nov. 

 Plate XII, Figures 1-3. 



The name Ba'ena cephalica is given to a fine skull which 

 belongs to the Yale University Museum, and which was col- 

 lected in the Laramie deposits of Converse County, Wyoming, 

 by Professor J. B. Hatcher. The specimen bears Professor 

 Marsh's receipt number 2110. 



In general form the skull is broad behind, and flat above, 

 with pointed snout. The length from the snout to the occipital 

 condyle is 67 mm ; to the end of the supraoccipital spine, 74 mm . 

 The greatest breadth, just in front of the tympanic chambers, 

 is 65 mm . From these chambers the width diminishes to the 

 snout. There is first a convexity in the outline, which ter- 

 minates at the hinder end of the maxilla ; a second and longer 

 one which ends behind the premaxilla, and a third one which 

 ends at the premaxillary symphysis. The flat upper surface 

 of the skull descends each way to the perpendicular sides. The 

 sides of the face about the orbits look upward and outward, as 

 well as forward. The tympanic opening is nearly circular, 

 19 mm in perpendicular and 15 mm in horizontal axis. The orbit 

 is circular and small, its diameter being 14 mm . The nasal open- 

 ing, as seen from in front, is somewhat heart-shaped, and is 

 directed upward and forward. From the orbit to the tympanic 

 opening is 24 mm ; from the nares to the orbit is 10 mm . 



The temporal region is roofed over, not so extensively as in 

 some undescribed Bridger skulls of the same genus. On each 

 side of the supraoccipital, this roof is excavated as far as a line 

 joining the anterior borders of the tympanic chambers. The 

 hinder end of the postfrontal is interposed between the parietal 

 and the squamosal. 



In general, the sutures of this skull are very distinct, but no 

 trace has been found of those between the frontals and the 

 parietals. There are distinct nasals. The prefrontal of each 

 side joins the postfrontal, so that the area of the frontals is 

 excluded from the orbit. The postfrontal is large, having a 

 length of 32 mm . The jugal is small, having a length of only 

 8 mm and a height of 15 mm . The squamosal forms the hinder 

 border of the tympanic opening. Superiorly it has a thin crest, 

 a relic of the former backward extension of the temporal roof. 

 There is a prolongation of the tympanic chamber into this bone. 

 The lower border of the zygomatic bar is considerably exca- 



