202 



1054. The shell of the Areolated Tortoise (Testudo areolata, Thunb. ; Homopw, 

 Burn.). 



Fig. Schsepff, Test. tab. 23. 

 Hab. Africa, Madagascar. 



Mm. Leverianum. 



Series of parts illustrating the principal Osteological characters distinguishing the 

 Tortoises, Terrapenes, and Turtles, or the Land, Freshwater, and Marine 

 Chelonia. 



1055. The skull of the green Turtle (Chelone mydas), without the lower jaw. 



The chief characteristics of this form of Chelonian skull, with the purposes which they 

 serve, have been noticed in the descriptions of Nos. 769, 774 and 776. 



Hunterian. 



1056. The skull, wanting the lower jaw, of the expanded Terrapene (Emys expansa ; 

 Podocnemis expansa, Wagner). 



This species differs from other freshwater Tortoises (Terrapenes), and approaches the ma- 

 rine Tortoises (Turtles), by the vaulted bony roof arching over the temporal depressions. 

 This roof is chiefly formed by the parietals, but differs from that in the Turtles in being com- 

 pleted laterally by a larger proportion of the squamosal than of the postfrontal, which does 

 not exceed its relative size in other Terrapenes. The present species further differs from the 

 marine Turtles in the non-ossification of the vomer and the consequent absence of a septum 

 in the posterior nostrils ; in the greater breadth of the pterygoids, which send out a com- 

 pressed rounded process into the temporal depressions : the orbits also are much smaller, and 

 are bounded behind by orbital processes of the postfrontal and malar bones : the mastoids 

 and paroccipitals are more produced backwards, and the entire skull is more depressed than 



in the Turtles. 



Presented by Lieut. Mawe, R.N. 



1057. The skull of a Terrapene (Emys concentrica). 



In this skull, which may be regarded as the type of that of the freshwater Tortoises, the 

 parietal crista is continued into the occipital one without being extended over the temporal 

 fosste ; the fascia covering the muscular masses in these fossae undergoing no ossification. 

 The bony hoop for the membrana tympani is incomplete behind, and the columelliform stapes 

 passes through a notch instead of a foramen to attain the tympanic membrane. The mastoid 



is excavated to form a tympanic air-cell. 



Hunterian. 



