left side, and a large part of the plastron. The length of the carapace is conjectural, but it 

 appears to have been at least 300 mm. The width was 220 mm. Its composition can not be 

 determined, since the bones have co-ossified and obliterated the sutures. In the median region 

 the bones reach a thickness of from 10 to 13 mm. The outer surface is smooth. The sulci are 

 narrow and shallow, and in most places are not traceable. The second, third, and fourth 

 vertebral scutes varied from 65 to 70 mm. in width. The first and fifth were probably somewhat 

 wider. 



The hinder extremity of the plastron (plate 8, fig. 2; text-fig. 39) is missing, so that its 

 form can not be determined. The anterior lobe has the right border nearly complete to 



beyond the midline in front, so that its form is known. 

 The dimensions of the plastron are shown in the 

 accompanying table. In order that the distinctness of 

 the species from B. hatcheri may be seen, the dimensions 

 of the latter are added. 



The plastron is somewhat concave. The concavity 

 extends laterally to a rounded ridge which runs from the 

 outer border of the anterior lobe to the outer border 

 of the posterior lobe. From this ridge the outer ends 

 of the hyoplastron and hypoplastron extend upward 

 and outward to the peripherals, and the elevation is 

 continued on the latter to the carina which unites the free borders of the third and the seventh 

 peripherals. From the midline of the plastron to the ridge is 55 mm.; from the ridge to the 

 lateral carina is about 85 mm., the measurements being taken on the mesoplastron. 



Most of the sutures of the plastron may be traced. The limits of the entoplastron are 

 not determinable; nor have the sutures between the xiphiplastra and the hypoplastra been 

 observed. The mesoplastra meet along the midline for about 23 mm. while their outer ends are 

 65 mm. wide. The sutures between the plastral bones and the bridge peripherals are distinctly 

 shown. The whole width of the plastron, on the mesoplastra, and following the curves, is 

 215 mm. 



The gular scutes appear to have met for some distance along the midline. The gulo- 

 humeral sulcus runs nearly directly across the lobe and meets the median line 27 mm. behind 

 the anterior border. The following are the antero-posterior dimensions of the various plastral 

 scutes, measured along the midline: Intergulars, 17 mm.; gulars, 10 mm.; humerals, 46 mm.; 

 pectorals, 50 mm.; abdominals, 47 mm.; femorals, 53 mm.; anals, 45 mm. On the bridge 

 there are 4 inframarginals, of which the inguinal is the largest, and the axillary somewhat the 

 smallest. The outer borders of these overlap on the bridge peripherals. 



This species appears to differ from Baena hatcheri in the smaller plastron, the longer 

 bridge, and the greater thickness of the bones of the carapace, especially of the dorsal region. 

 It is named in honor of Professor O. C. Marsh, formerly professor of vertebrate paleontology 

 in Yale University. 



Baena hatcheri Hay. 



Plates 9, 10; text-figs. 40, 41. 



Baena hatcheri, HAY, Ann. Carnegie Museum, i, 1901, p. 325, plate xv. HATCHER, Bull. U. S. Geol. 

 Surv. No. 257, p. 79. 



The type of the species is a very complete shell which was collected by Mr. J. B. Hatcher, 

 in the year 1900, in the Ceratops beds of the Laramie formation, in Converse County, 

 Wyoming. The locality given more particularly is a sandstone bluff on the south side of 

 Lance Creek, opposite the mouth of Dolgie Creek. The specimen belongs to the collection 

 of the Carnegie Museum. 



The whole plastron is present and all of the carapace except a small portion of the rear. 

 The sides of the carapace are somewhat crusht in, and some crushing has been suffered by the 

 bridge peripherals; but these defects do not stand in the way of determining the characters of 

 the species. It displays all the epidermal sulci and nearly all of the bone sutures. Moreover, 

 the matrix, a soft sandstone, has been removed, so that the interior too can be observed. 



