148 THE WASATCH AND BRIDGER FAUN^. 



than half as long. Tlie posterior lobe is truncate at the extremity. The 

 nuchal scute projects beyond the first marginal ; the reverse is the case in 

 the type of B. hebraka. The posterior sutures of the intergular and gular 

 scuta have a common center, and that of the gular has a rectangular curva- 

 ture, the nearly transverse middle portion slightly convex forwards. The 

 suture separating the femoral and anal scuta is similar, but reversed in 

 direction, presenting two obtuse right angles, two portions being transverse 

 and one longitudinal on each side. 



The Baiina undata is quite similar to the B. arenosa in most respects. As 

 in Leidy's specimens, the sutures of the plastron in the B. arenosa are obliter- 

 ated in my single specimen, while in several of the B. undata they leave 

 distinct traces even when coossified. As the latter are of larger size than 

 the former, the diflference in this respect cannot be due to age. Besides, the 

 plastron is smoother and presents no median carina. It is more roughened 

 posteriorly with small irregular tubei'cular ridges. Traces of the grooves 

 seen in B. arenosa are found on the anterior median region. The peculiar 

 fifth or anterior costal scute is similar to that of B. arenosa, as are the gular 

 and intergular scutes. In fact, the resemblances between this species and 

 the B. arenosa are so close that I suspect that when we come to know the 

 younger stages of the latter we will find that the intersternal bones are 

 present, as in the B. undata. On this ground I have not adapted the genus 

 Chisternum proposed by Dr. Leidy for the latter on account of the presence 

 of the intersternals. 



Baena undata is more abundant in the Bridger beds than any other 

 species of the genus. I found it on Black's Fork and elsewhere. 



Baena arenosa Leidy. 



Proceed. Acu<l. Phila., 1870, p. IM'J. Keport U. S. Geol. Surv. Tuits., i, p. 161, pi. xvi an<l xx, figs. 1-5 

 anrl xiii. 11. affniis Leidy, ADnunl Report U. 8. Geol. Surv. Teirs., 1871, p. 367. 



Plate XVIII, figs. 1-2. 



A perfect specimen of this species is of smaller size than those of the 

 preceding, and about equal to the Bseudcmys rugosa, and not dissimilar in 

 form. 



The carapace is strongly convex, and all its component parts, as well 

 as those of the plastron, are coossified. The sutures of the intersternal 



