TESTUDINATA. 145 



but differs in the presence of an intersternal bone on each side, as in the 

 Pleurodira. As generic characters it possesses two marginal intergular 

 plates, which resemble the gulars of Emydidce. It has a series of inter- 

 marginal scuta. The free lobes of the sternum are narrowed and shortened 

 and the bridge is very wide. The dermal scuta are everywhere distinct. 

 The mesosternal bone is in form between T-shaped and sagittate. The 

 last pair of marginals, instead of being in contact, are separated by a wide 

 emargination. 



The preceding characters were first noticed by Leidy. Another one 

 appears in my specimens of B. arenosa, B. undata, and B. hebraica, which 

 Dr. Leidy does not mention, viz, the presence of five costal scuta instead 

 of four. The accessory one is anterior, and is taken from the usual first 

 costal and first vertebral, both of which are contracted in consequence. 

 Leidy's specimens are damaged in the region in question, and do not dis- 

 play anything. The character is unique in the order Testudinata, unless it 

 be found in the Platychelys of the European Jurassic, which is one of the 

 Baenidx 



The afiinities of this genus are complex and interesting. It would be 

 a pleurodire, but for the fact that the pelvis is not coossified with the plastron; 

 nevertheless there are rudiments of this union in the form of a shallow pit 

 on each side. The posterior or ischiadic is near the posterior end, and on the 

 lateral mai-gin of the post-abdominal bone ; it is of a naiTow, oval form. 

 The anterior is shallow and sublaterally impressed into the side of the 

 upright septum which supports the carapace. Whether it received the 

 pubis or not is uncertain. 



The double intergular scute is not found in any existing genus of 

 Pleurodira, but exists in Tropidemys Riitim. of the Jurassic. 



The posterior margin of the carapace is excavated as in Chelydra, but 

 the margin is more arched in this position. This form in Baena suggests 

 the presence of a large tail, and the sen-ate margin of the carapace posteri- 

 orly reminds one again of Chelydra. There ai-e in B. arenosa fourteen mar- 

 ginal scuta without the nuchal; in Chelydra serpentina, as in Emydidce, but 

 thirteen. 



There are prominent axillary and inguinal septa, as in some Emydidce^ 



