PROTOSTEGIDiE. 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 ot pairs ot 

 peripherals. 



The estimated total length of the carapace, exclusive of the nuchal, is 1.7 meters; with the 

 nuchal, it was probably about 1 .0 meters. The width, exclusive of the peripherals, must have 

 been about 1 meters; including the peripherals, about 2.5 meters. 



The neurals are mostly broader than long. Their borders are furnisht with long and 

 coarse dictations, which interlock with others from the contiguous neurals and costal plates. 

 It is difficult, 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- 

 sisted each of paired bones. He concluded also that the longi- 

 tudinal groove was filled with horny materials and that the animal 

 may have borne a row of dorsal spines. The last one or two 

 neurals and the suprapvgals have not been well determined. 

 Little can be said concerning the pygal. Indeed, the terminal 

 bone shown in Wieland's figures of the carapace is probably a 

 suprapygal. 



The ribs and the costal plates resemble much those of Pro- 

 tostega. The disk formed of the costal plates and the neurals is 

 much reduced, extending outward from the median line hardly 

 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-fouiths 

 as long as the second. Its length is 740 mm.; its diameter, about 75 mm. The other ribs have, 

 in the tvpe 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. In a later paper (Amer. Jour. Sci., xv, p. 211) 

 he states that the inner borders of these bones are strongly digitated. 



The plastron | \mer. four. Sci., v, p. 16) has the same general structure as that of Pro- 

 ., altho the principal bones appear to have been broader and to come nearer filling up the 

 median fontanel (fig. 262). \s represented by Wieland, the digitations bordering them are 

 extraordinarily numerous and elongated. The T-shaped entoplastron (fig. 262, eni) 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 ot Protostega. The extremities of the wings are 280 mm. 

 wide. They appear in the figure to occupy their natural position on the hyoplastra. The 



