. Carnegie Institution of Washington publication. . Figs. 656 and 637.—Plastomenus vzsenaus. X \. 6:6. Cara pace. 657. Plastron. were not developt. The nuchal has a lateral extent of 90 mm.; and a fore-and-aft extent of 20 mm. Its outer ends neither overlap nor underlap the anterior border of the first costals. These costals are somewhat narrower at their distal ends than at the proximal. The other costals, except the seventh, are wider at the outer ends than proximallv. The seventh costals are much wider along the midline than any of the others, and form a large part of the rear of the shell.
. Carnegie Institution of Washington publication. . Figs. 656 and 637.—Plastomenus vzsenaus. X \. 6:6. Cara pace. 657. Plastron. were not developt. The nuchal has a lateral extent of 90 mm.; and a fore-and-aft extent of 20 mm. Its outer ends neither overlap nor underlap the anterior border of the first costals. These costals are somewhat narrower at their distal ends than at the proximal. The other costals, except the seventh, are wider at the outer ends than proximallv. The seventh costals are much wider along the midline than any of the others, and form a large part of the rear of the shell. Thev extend along the midline a distance of 50 mm., and laterally from the midline a distance of 75 mm. The edges of the carapace are rounded or cut off rather abruptly. The thickness of the costals at the free edges is about 5 mm. The only neural which is complete is the third. It has a length of 18 mm. and a width of 12 mm. posteriorly. The ornamentation consists of a number of longitudinal welts and of numerous pits. Of the welts there are about 10 on each side. These resemble a series of waves, those near the midline being somewhat nearer together than those near the borders of the carapace. On the hindermost costals the weirs are sharper and somewhat broken up into elongated nodules. On the nuchal and costals of the first pair the welts are obsolete. The pits are rather shallow and are separated by ridges which are rounded or flat on their summits. There are 5 or 6 of the pits in a line 10 mm. long. The)' are less distinct on the neurals and the proximal ends of the costals. On the outer halves of most of the costals the pits are arranged to a great extent in lows, parallel with the axis of the animal or with the adjacent free border of the carapace. Of the plastron (plate 87, fig. 2; text-fig. 637) the entoplastron, both epiplastra, and a small portion of the left hypoplastron are missing. The parts present are shown on the plate. Please note that these images are extr
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