EOCENE TESTDDINATA. 
55 
The posterior surface is on the fifth and sixth costals, chiefly on the former, 
where it terminates two-fifths the length from the distal end. The iliac 
sutural surface is I’ather small, and is situated near the proximal extremity 
of the eighth costal bone, half-way between its borders. It is a subtrian- 
gular tuberosity, with a projecting narrow capitulum directed toward the 
proximal apex of the costal bone. 
The free marginal bones are large, thin, and but little recurved; the 
second and eleventh ' being the most so. The anterior marginals are very 
little smaller than the posterior. They are all crossed proximally by 
the costo-marginal suture, excepting the caudal marginal. The bridge- 
marginals are thin, not angulate, and but little convex, indicating that the 
body-cavity is not depressed. The angle of the marginals adjoining the 
bridge is somewhat recurved. 
The bones of the plastron are not thick, and are united by rather fine 
suture. The anterior lip is not very prominent, is truncate, and is notched 
just within its external angles. The mesosternal bone is produced anteri¬ 
orly, while the posterior border is transverse, and the extero-posterior angles 
obliquely truncate. The common hyosternal suture is a little longer than 
the common hyposternal. The posterior lobe contracts distally, and termi¬ 
nates in two points, which are separated by a semicircular emargination. 
The superior margin of the plastron is thickened at the extremity of the 
anterior lobe in front of a definite line, which extends between the extero- 
posterior angles of the episternal bones. Of this thickening, two parallel 
ribs, which extend to the lateral angles of the lip, are most prominent. 
Behind the episternal bones, the thickening is little marked. The superior 
border of the entire posterior lobe exhibits a wide thickening, with sharply- 
defined inner border, which is most elevated opposite the posterior angles. 
The dermal scuta are well marked. The first vertebral is longer than 
wide, the second as long as wide, the third a little wider than long, and 
the fourth still wider. The nuchal scutum is distinct, and is notched behind.' 
The gular scuta are longer than their combined width, and they extend 
well on the mesosternal. The humero-pectoral suture is nearly transverse, 
and passes behind the mesosternal bone. The abdominal scuta are longer 
than the pectoral, but not much; the length of the femoral on the middle 
