Hav : I'Kor.AENA Gen. Nov. 203 



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

 which covered the bridge cannot be mapped with certainty, but there 

 can be bttle doubt that they were present and mucli like those o{ Ba'nui. 



This genus is certainly closely related to Ba'nia, and it may be ques- 

 tioned whether it would not be better to refer the species to this genus. 

 Most of the characters given imder the definition of the genus are 

 hardly of generic value ; but considering the many minor differences 

 between the species and those of Baena, and the length of the period 

 intervening between the Morrison epoch and the IJelly River and 

 Laramie epochs in which the earliest species of Bacna are found, it 

 seems ])robable that a complete skeleton would afford more satisfactory 

 generic characters. 



It seems at least very certain that P. sculpta is to be regarded as a 

 form ancestral to the later numerous species o{ Ba'aia which have been 

 found in Belly River, I'pper Laramie, Puerco, Bridger and Uinta beds. 

 Dr. Baur regarded Co/npsei/iys plicatiilus as the forerunner of Ba'cfia 

 {Proc. Acad. N'ai. Sci., Phila., 1891, p. 421); but we now find in the 

 same quarry from which C. plicatiilus has been reported a form much 

 nearer to Bacna than is Compsemys. It becomes evident that we must 

 go back much further to find the common ancestor of Co/npscmys and 

 Proba'cna. 



Plafyche/ys, of the Upper Jurassic of Solothurn, Switzerland, is 

 evidently very closely related to Bacna and Probacna, and has been 

 very properly assigned by Lydekker to the Pleurosternidai. It differs 

 in having a more highly sculptured carapace, supramarginal scutes, and 

 mesoplastrals which do not reach to the midline. 



In his Bibliography and Catalogue of the Fossil Yertebrata of North 

 America, p. 437, the present writer has adopted for this family the 

 name Pleurosternidai, having overlooked the fact that Cope employed 

 the name Baenidse as far back as the year 1873 (^^h Ann. Report U. 

 S. Geol. Surv. Terrs., p. 621). The writer is not aware that the 

 name Pleurosternidte has had an earlier use. 



Explanation of Plate. 



Fig. I. View of the carapace showing some of the vertebral and costal scutes and 

 the sculpture. 



Fig. 2. View of the plastron. The light lines indicate the sutures, the dark lines 

 the boundaries between the scutes. 



In both figures the anterior end of the shell is toward the left hand. 



