BAENID&. 67 
The vertebral scutes are relatively narrow, the second having a length of 88 mm.anda width 
of 65 mm.; the third a length of 85 mm. and a width of about 70 mm.; the fourth a length of 
80 mm. ead a width of 70 mm.; the fifth a length of 48 mm. and a width of 80 mm. In the 
case of the first vertebral the same lack of symmetry is to be seen as has been observed in so 
many other specimens belonging to the genus Baéna. 
The costo-marginal sulci are distant from the edge of the carapace about 22 mm. Those 
subdividing this anterior marginal region are too obscure for certain determination. There 
are indications of one which crost this region about 15 mm. to the left of the midline. There 
was, therefore, probably a nuchal scute 30 mm. long from side to side. Beyond this the 
marginals increase in length and breadth. Over the bridge they rise on the sides of the 
carapace 45 mm. 
On the plastron are distinct gulars and intergulars. The humero- pectoral sulcus crosses the 
midline on the line joining the axillary notches. Laterally the sulcus is suddenly turned forward 
and outward. The pectoral scutes meet along the midline for a distance of 53 mm., and extend 
laterally about 72 mm. The abdominal scutes occupy 52 mm. of the midline; the femorals 67 
mm.; the anals 50mm. As in other species of Baéna, the suture between the femorals and the 
anals runs outward, then turns backward for some distance, then again outward. 
There are 4 large inframarginals. 
Baéna arenosa Leidy. 
Plate 12; plate 13, fig.1; plate 14, figs. 1-3; text-figs. 44-51. 
Baéna arenosa, Letpy, Proc. Acad. Nat. Sci. Phila. 1870, p. 123; U. S. Geol. Surv. Wyoming, etc., 
1870 (1871), p- 367; U. S. Geol. Surv. Montana, etc., 1871 (1872), p. 368; Contrib. Ext. Vert. 
Fauna W. Terrs., 1873, pp. 161, 343, pl. xiii, figs. 1-3; fpl. xv, figs. 1-5; pl. xvi, figs. 8, 9. —Copr, 
?Append. LL of Ann. Report Guick of Engineers, 1875, p. 96; ?Wheeler’s Surv. rooth Merid., 
1877, p. 52, pl. xxiv, fig. 32.—Baur, Proc. Acad. Nat. Sci. Phila. 1891, p. 426, fig—Hay, 
Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 437. 
Baéna affints, Leroy, Ann. Report U. S. Geol. Surv. Wyoming, etc., 1870 (1871), p. 367. 
Baéna arenosa, the type of the genus Baéna, was based on a shell lacking only the anterior 
lobe of the plastron and the anterior border of the carapace. This specimen is now in the 
United States National Museum at Washington. It was figured and described at length in Dr. 
Leidy’s work of 1873. The specimen was obtained in the Bridger deposits, at the junction of 
the Big Sandy and Green Rivers, in southwestern Wyoming. These beds are regarded as 
belonging to the lowermost of the Bridger formation. 
The specimen described by Leidy evidently had originally a length of close to 340 mm. and 
a width of 288 mm. The rear of the carapace is broadly rounded: The vertebral scutes are 
broader than long. The hinder lobe of the plastron is broad and it narrows slow ly backward. 
The width of the anterior lobe, taken from the outer ends of the humero-pectoral sulci, equals 
half the length of the plastron behind this. Dr. Leidy states that the position of the former 
sutures can not be detected. This is true as regards the outer surface of the bones; but on the 
upper side of the plastron the sutures on each side of the mesoplastrals are to be observed. 
The left mesoplastron had a width of about 25 mm. at the midline; that on the right side was 
narrower. 
A portion of the pelvis and the sacral vertebra and ribs of this specimen were figured by 
Dr. Leidy. Later, Dr. Baur obtained from the matrix of the specimen additional parts of the 
pelvis and briefly described them. While some parts are still wanting there is enough to show 
that the ischia were united with the pubes along the midline and that the pubes extended at 
least 35 mm. in front of their hinder border at the midline (figs. 44, 45). The upper end of 
the illum was expanded backward. The width of this expanded part was equal to the height, 
35 mm. 
The writer follows Dr. Leidy and Professor Cope in identifying the former’s B. ajfinis as 
the earlier described B. arenosa. The original description of B. affinis was exceedingly brief and 
hesitating. It was supposed to be distinct from B. arenosa because of the presence of only 
3 inframarginals. In Leidy’s next reference to the species, he referred it to his earlier B. 
arenosa. The type is now in the collection of the Philadelphia Academy. It was 
