PROTOSTEGID. 203 
the Judith River formation. The species was probably the largest that is at present known 
to have existed. From the length of the neck and the carapace Wieland estimates that the 
total length of type specimen was about 3.5 meters. Specimen in Yale University collection. 
Of the remains of this great turtle the present writer has studied only the skull. The 
greater part of the description here given has been derived from Wieland’s papers. The 
figures are reproduced from those papers. Fig. 260 represents the carapace as shown in 
Wieland’s latest restoration of it (Amer. Jour. Sci., xv, p. 212). In this figure (p. 189) a large 
bone is shown in front as the nuchal but which the present writer regards as the entoplas- 
tron. This figure is based on the type specimen, except that the first rib is added from 
another individual. The carapace, so far as is known, was composed of 8 neurals, 1 or 
more suprapygals, 10 pairs of ribs, a nuchal, a pygal, and an undetermined number of pairs of 
peripherals. 
The estimated total length of the carapace, exclusive of the nuchal, is 1.7 meters; with the 
nuchal, it was probably about 1.9 meters. The width, exclusive of the peripherals, must have 
been about 2 meters; including the peripherals, about 2.5 meters. 
The neurals are mostly broader than long. Their borders are furnisht with long and 
coarse digitations, which interlock with others from the contiguous neurals and costal plates. 
It is difhcult, therefore, to determine the widths of the neurals, but these widths may be taken 
as from 175 mm. to 225 mm. The neurals are relatively thin, being only about 5 mm. The 
median line of most of the neurals is markt by a deep and narrow groove, which becomes 
widest at the center of the neural. From this center there radiate outward characteristic 
surface striations. In his first description Wieland thought that these neurals probably con- 
2 sisted each of paired bones. He concluded also that the longi- 
Width at tudinal groove was filled with horny materials and that the animal 
Rib. Length. 
middlepart. may have borne a row of dorsal spines. The last one or two 
7 neurals and the suprapygals have not been well determined. 
; oe . Little can be said concerning the pygal. Indeed, the terminal 
A 7525 78 bone shown in Wieland’s figures of the carapace is probably a 
5 1020 75 suprapygal. 
: bees a The ribs and the costal plates resemble much those of Pro- 
8 = 60 tostega. he disk formed of the costal plates and the neurals is 
2 = 35 much reduced, extending outward from the median line hardly 
os =) 
one-fifth the distance to the ends of the ribs Beyond the borders 
of the disk the ribs are wholly free from one another. The first 
rib is extraordinarily large, as compared with the same rib in other turtles, being three-fourths 
as long as the second. Its lengthis 740 mm.; its diameter, about 75 mm. The other ribs have, 
in the type specimen, the dimensions shown in the table. 
Where the ribs emerge from the disk their thickness averages only about 25 mm. It is 
thus seen that they increase much in thickness toward the middle of their length. 
The bone described by Wieland (Amer. Jour. Sci., v., 1898, p. 17) as the nuchal (fig. 261) 
and now regarded by the present writer as such, is roughly triangular, with a concave anterior 
border. The lateral extent of the bone is 640 mm.; its antero-posterior extent, 250 mm. On 
the inferior surface there is a trapezoidal elevation, which Wieland regarded as having afforded 
an articulation with the last cervical vertebra. The thickness through the elevation is 35 mm.; 
elsewhere, from 10 mm. to 15 mm. 
Little has yet been publisht about the peripherals. A fragment of one was figured by 
Wieland in his earliest description of this turtle. Ina later paper (Amer. Jour. Sci., Xv, p. 211) 
he states that the inner borders of these bones are strongly digitated. 
The plastron (Amer. Jour. Sci., v, p. 16) has the same general structure as that of Pro- 
tostega, altho the principal bones appear to have been broader and to come nearer filling up the 
median fontanel (fig. 262). As represented by Wieland, the digitations bordering them are 
extraordinarily numerous and elongated. The T-shaped entoplastron (fig. 262, ent) has a 
breadth of 940 mm. and a length of 450 mm. The anterior border is concave to the outer 
extremities, thus differing from that of Protostega. The extremities of the wings are 280 mm. 
wide. They appear in the figure to occupy their natural position on the hyoplastra. The 
