768 - THE WHITE EIVER FAUNA. 



The T. amphitliorax agrees in many respects with the T. Ugonius, but 

 difi'ers much in the characters of the anterior lobe of the plastron. There 

 is scarcely any lip, but the margin is truncate, with a bounding angle on 

 each side to represent the usual margin of the lip. In one specimen this 

 angle is much rounded. The inferior surface differs from that of T. Ugonius 

 in being without impressed groove in the line of the gular suture and median 

 fossa. In these respects it resembles T. laticuneus. One anterior lobe was 

 found with the posterior lobes of two individuals, which are exactly alike. 

 This lobe was deeply emarginate, and each sublobe is broadly rounded, 

 wedge-shaped, with thin edge, with a notch in it at one point. The margin 

 becomes very thick near the groin. 



The relations of the inferior and superior bounding gular scuta are dif- 

 ferent in this species from what is seen in T. Ugonius. The superior groove 

 has the posterior position appropriate to a long lip, Avhile the inferior leaves 

 the margin much anterior to that point, and just posterior to the angle which 

 bounds the very short lip which the species actually possesses. The two 

 sutures nearly correspond in position in the T. Ugonius. The pectoral 

 scutum is quite narrow in the specimens, as in T. Ugonius. The scutal 

 sutiires are impressed and do not have raised borders. The edges of the 

 marginals are all injured in the specimens. The mesosternal bone is a little 

 wider than long. It is more contracted anteriorly than posteriorly, but the 

 lateral angles are about opposite the middle of the length. 



The costal and vertebral bones are rather thin. A marginal bone, 

 probably one of those in contact with the anal, has a peculiar form, such as 

 does not exist in any other species, unless it be the T. Ugonius and T. quad- 

 ratus, where I have not seen it. It is recurved at the sutural edges, or is con- 

 cave at the middle, so as to be openly trough-shaped. This indicates a very 

 convex anal marginal bone, and a doubly sigmoid flexure of the free margin 



behind 



Measurements. 



No. 1. 



M. 



Widtt of truncate lip 080 



Width of humeral scute fore and aft 024 



Length of posterior lobe on axial line of a half 151 



Width of base of posterior marginal lobe of plastron 092 



Length of axial of trough- shaped marginal (anteroposteriorly) 072. 



