BAENIDiE. 



59 



little or not at all notcht, except in the midline behind, where there is a slight excavation. 

 In the nearly smooth hinder border this genus differs from the species of Ba'ena. 



Most of the sutures and of the epidermal sulci are obscure; and in most parts of the cara- 

 pace the sutures are incapable of determination. The sulci bounding the second, third, and 

 fourth vertebral scutes are satisfactorily seen. These scutes were very broad, each about 34 

 mm.; while the costal scutes were only about halt as wide. The areas occupied by the median 

 scutes are conspicuously sculptured. The sculpture, as shown by the third scutal area, con- 

 sists of ten or twelve prominent, sharp, uneven ridges, which radiate forward and outward 

 from the middle of the hinder border of the area. Evidently a somewhat similar, but less bold, 

 sculpture characterized the areas of the costal scutes; but these surfaces have been injured so 

 that it can not be described. There is no evidence of the presence of supramarginal scutes. 



On the left side the costal and marginal plates are broken away. The anterior and 

 posterior buttresses of the plastron are thus revealed; and it is evident that the anterior one, 

 joining the second costal plate, projected inward a considerable distance, as in Ba'ena, to form 

 the anterior boundary of a lateral chamber, whose posterior boundary was formed by the 

 hinder buttress joining probably the sixth costal plate. 



When the costal plates broke away, the extremities of the third, fourth, and fifth ribs were 

 left adhering in the matrix. These evidently past downward deeply against the inner sides of 

 the corresponding marginal plates, as in Chelydra. Such was probably not the condition in 

 Ba'ena. The ends of the ribs are terete, not flat as in most other cases. So far as can be deter- 

 mined, there were no fontanels between the costal plates and the marginals. 



Of the plastron (plate 7, fig. 5) all is present except the epiplastrals, and possibly the 

 anterior part of the entoplastron. The plastron resembles closely that oi [Ba'ena; but the hinder 

 lobe is not notcht posteriorly, but rounded. There is a considerable fontanel between the inner 

 ends of the mesoplastra. This may be due to the immaturity of the specimen; but judging 

 from the closeness of all the sutures of our specimen, and from the fact that in Ba'ena the bones 

 soon co-ossify, it seems probable that the fontanel would persist till a late period of life. 



The anterior as well as the posterior lobe has a width at the base of 36 mm. The posterior 

 has a length of 30 mm., and the anterior was probably about as long. The posterior lobe 

 diminishes in width rather rapidly backward. The entoplastron was unusually long and narrow 

 in its hinder portion. Nothing can be determined regarding the intergular and gular scutes. 

 The mesoplastron is narrowed at the inner end, as in some species of Ba'ena. Each is 

 traverst by the pectoro-abdominal sulcus. 



The bridge is 30 mm. wide, fore and aft. The inframarginal scutes which covered the 

 bridge can not be mapt with certainty, but there can be little doubt that they were present and 

 much like those of Ba'ena. 



P. sculpta may be regarded as a form ancestral to the later numerous species of Ba'ena 

 which have been found in Belly River, Upper Laramie, Puerco, Bridger and Uinta beds. Dr. 

 Baur regarded Glyptops plicatulus as the forerunner of Ba'ena (Proc. Acad. Nat. Sci. Phila. 

 1 89 1, p. 421); but we now find in the same quarry from which G. plicatulus has been reported 

 a form much nearer to Ba'ena than is Glyptops. It becomes evident that we must go back much 

 further to find the common ancestor of Glyptops and Proba'ena. 



Platychelys, of the Upper Jurassic of Solothurn, Switzerland, is closely related to Ba'ena 

 and Proba'ena, and has been assigned by Lydekker to the Pleurosternida?. It differs in having 

 a more highly sculptured carapace, supramarginal scutes, and mesoplastrals which do not 

 reach to the midline. 



Genus BAENA Leidy. 



Shell firmly joined to the carapace by sutural union with the lateral peripherals and by 

 broad and high axillary and inguinal buttresses. Hinder border of the carapace scallopt, and 

 with an extensive excavation over the tail. Nuchal bone in contact with the first neural; no 

 preneural; no supramarginal scutes; anterior lobe of plastron not extended in front of the 

 carapace. Mesoplastra large, with the outer ends expanded. Posterior plastral lobe slightly 

 emarginated. Intergulars, gulars, and inframarginals present. Skull broad, with the temporal 

 region extensively rooft, the squamosals in contact with the parietals. Jugal forming a part of 



