1G8 



Comparative measurements of the anterior extremity of the plastron, where 

 this is present in the specimens, are as follows: 



Length of plastron to anterior pectoral 

 groove 



Breadth of plastron at anterior pectoral 

 groove 



Breadth of plastron at anterior humeral 

 groove 



Breadth of plastron at middle gular 



groove 



First 

 specimen. 



Lines. 



44 



.Second 



specimen. 



Lines. 

 34 

 36 



28 

 18 



Third 

 specimen. 



Lines. 



30 



42 

 28 

 18 



Fourth 



specimen. 



Lines. 



61 



14 

 34 



20 



Sixth speci- 

 men, young. 



LllltS. 



20 

 13 



The pelvis is more expanded above than in Emys, and in this respect is 

 more like that of the snapper. The sacrum represented in Fig. 9, Plate 

 XVI, is intermediate in its proportions to that of the two genera just men- 

 tioned. 



The length of the sacral vertebras of Baena, independently of the wings or 

 transverse processes, exceeds the breadth, the proportions in this respect 

 according more with the condition in the terrapin than in the snapper. The 

 second sacral vertebra is, however, larger than the first, as in the latter turtle, 

 and the reverse of what it is in the former. The inferior surface of the 

 bodies of the sacral vertebras is half cylindroid, depressed at the sides in the 

 first one, but scarcely so in the second. 



The anterior articular surface of the first sacral centrum is moderately 

 convex ; the posterior articular surface of the second centrum is concave. In 

 Emys the corresponding surfaces are flat, or nearly so; in Chelydra the ante- 

 rior one is concave, the posterior convex, with lateral extensions nearly flat. 



The proportionate length and robustness of the sacral alas of Baena agree 

 more nearly with the condition in the snapper than in the terrapin. In Emys 

 the posterior alas are comparatively feeble appendages, and they join the ends 

 of the anterior alas by means of a ligament. In Baena the posterior alas are 

 strong processes, as in the snapper, and likewise, as in this, join the ends of 

 the alas in advance by suture, but appear not to be prolonged to join the 

 ilium. 



The innominatum of Baena, as represented in Fig. S, Plate XVI, is propor- 



