358 AMERICAN TESTUDINATA. Part II. 



the free edges above and below project beyond the attached surface of the body. 

 The middle region is the part entirely encircled by the shield. As this region 

 is here so predominant, the plastron is longer and broader under it, and its 

 suture with the carapace longer, and the openings about the ends shorter, than 

 in the Emydoidoe. The other parts of the plastron, that is, the parts which under- 

 lie the regions at the ends, are comparatively short and small, narrowing rapidly 

 towards the ends of the body ; indeed, they are so reduced as to aj^pear like mere 

 projections; they are both turned out of the general level of the lower surface, the 

 front one turned up and the hind one turned down. The hind one does not under- 

 lie the whole of its region, but the body projects beyond it all around the sides and 

 hind end, so that the opening is outside as well as above it. There is a broad 

 space between its outer end and the carapace behind ; and, when it is longest, 

 this end is deeply notched. The projecting free edges of the carapace flare outr 

 ward over these openings. Over the one about the hind end of the body, it flares 

 outward considerably at the sides, but less and less backward, until, just behind 

 the tail, it continues the steep descent of the caraj)ace above, directly down, and 

 reaches nearly or quite as low, and often lower, than the general level of the 

 plastron. 



The shield is entirely ossified, and the general arrangement of all the bony 

 plates is similar to that which we find in the Emydoidte ; but the marginal plates 

 are longer, and the two pairs in the plastron which are sutured to the carapace 

 larger, than in that fiimily. To meet the neck, the first one or two fixed vertebrae 

 are turned down more steeply than the carapace above ; the first one is in the 

 front margin of the body. Over the middle region, the column follows the general 

 direction of the carapace above, and with it turns aljruptly down, shortly before 

 reaching the sacrum, and continues in its steep descent through the latter, and to 

 the end of the tail. As the sacrum is so high up here, the vertebral column below 

 is necessarily very long, before it reaches the surface of the body ; it protrudes 

 but little, and the skin does not close around it till very near the end, so that 

 there is only a short, stubbed tail visible. The vertebrae of this part of the col- 

 umn are flattened on the upper and lower surfaces. 



The scapular arch is nearly perpendicular, and very high ; the acromion and 

 coracoid process are both short, and the shoulders not wide apart ; the humerus is 

 broad at the elbow joint, and the tibia and fibula make the forearm broad ; the 

 bones of the wrist, hand, and fingers, are all short and compact, and move but 

 little upon one another, or upon the end of the forearm. The fingers are all 

 close together, down to the last joints ; these joints protrude free, and are covered 

 with flat, sharp nails. When the muscles and skin are attached, the foot is kept 

 nearly on a plane with the forearm above, and the whole limb below the elbow is 



