. Carnegie Institution of Washington publication. !>.!•:. *33 Peripheral. Length. \\, [th. C ppei t,M i . Lowei [act Thickness. 1 "•1 do 17 2 82 do 21 3 75 61 4 -1. (,o •" 80 4 4- 6 85 112 41 7 91 Si 8 9 105 26 9 93 10s 14 IO 'IO 111 '4 1 1 83 110 and the eleventh, have each a pit in the inner face to receive the end of a rib extending beyond the costal plate. In the hinder peripherals these pits are flattened; also they produce notches in the upper face of a number of the hinder peripherals, as they do in 0. borealis. This deficiency in the upper wall of some of the
. Carnegie Institution of Washington publication. !>.!•:. *33 Peripheral. Length. \\, [th. C ppei t,M i . Lowei [act Thickness. 1 "•1 do 17 2 82 do 21 3 75 61 4 -1. (,o •" 80 4 4- 6 85 112 41 7 91 Si 8 9 105 26 9 93 10s 14 IO 'IO 111 '4 1 1 83 110 and the eleventh, have each a pit in the inner face to receive the end of a rib extending beyond the costal plate. In the hinder peripherals these pits are flattened; also they produce notches in the upper face of a number of the hinder peripherals, as they do in 0. borealis. This deficiency in the upper wall of some of the pits marks one difference between this species and 0. emarginatus, the type of the genus. The inner face of the second peripheral has a large pit for the reception of the outer anterior exten- sion of the hvoplastron. The inner face of the third, fourth, fifth, sixth, and seventh periph- erals is broad and longitudinally excavated. These bones have thus three borders, the outer, or free border; the upper border, which articu- lates with the costals; and the inferior border, which comes into contact with the plastron. In the anterior end of the eighth there is a cavitv into which the outer posterior process of the hypoplastron projects. The innei face of the peripherals behind the eighth becomes narrow and curves into the lower face. Thus, these hinder peripherals are thin and wedge-shaped. The dimensions of the peripherals are shown in the table herewith. The acute free border of the hinder peripherals may be traced forward on the more anterior ones, where it forms a keel separating the upper face from the lower. The peripherals, from the seventh to the eleventh inclusive, are slightly concave on the upper surface. • The pygal bone measures about 85 mm. along the tree border ami has a height of about 75 mm. The sulci between the various scutes of the carapace are rather deeply sunken. The dimensions of the vertebral scutes are given in the table. The hinder border of t
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