DISCOS A URUS. 



23 



excavated to its base into a transversely elliptical costal pit, bounded by a promi- 

 nent acute border. The pit occupies the middle portion of the body from above 

 downward, and extends two-thirds its length, reaching nearer the anterior than the 

 posterior articular surface. 



Measurements, derived from the two specimens which are almost identical in size 

 as well as form, are as follows : — 



Lines. 

 Length of body between the grooves defining the articular extremities . .19 

 Extreme length of body between the prominent margins of the articular extremities 24 



Breadth of articular extremities . .31 



Height of articular extremities 26 



Estimated breadth of spinal canal g 



Transverse diameter of costal pits 14 



Vertical diameter of costal pits . . . . . . . . . .11 



2. A vertebra, represented in Figs. 10, 11, 12, Plate V, rather larger than the 

 preceding, but nearly identical in form, from the lower Cretaceous of Mississippi, 

 presented to the Academy by Prof. M. Tuomey. In this specimen the articular 

 extremities of the body are nearly flat surfaces, being much less depressed towards 

 the centre and much less prominent towards the periphery than in the Alabama 

 specimens. It differs also from the latter in having the articular surfaces termi- 

 nating in an acute margin and not defined from the rest of the body by a groove. 

 The body beneath, Fig. 10, presents inflections apparently for the articulation of 

 chevron bones, those posterior being large, while those anterior are but slight. The 

 vertebral arch, partly preserved in the specimen, is coosified with the body. It 

 presents no conspicuous mark of its original separation, and a continuous slope 

 extends from the side of the arch upon that of the body to the upper margin of the 

 costal pit. 



The measurements of the specimen are as follows: — 



Lines. 

 Length of the body at the acute margins of the articular extremities . . .24 

 Extreme length of the body at the prominent periphery of the articular extremities 26 



Breadth of the articular extremities 36 



Height of the articular extremities 29 



Diameter of spinal canal 7 



Transverse diameter of costal pits ......... 15 



Vertical diameter of costal pits 9 



3. A much mutilated body of a vertebra from Choctaw Blufi", Clarke Co., Alabama, 

 presented by Prof M. Tuomey to the Academy. The specimen has the same form 

 as that just described, excepting that its articular faces are more concave and it is 

 considerably larger. 



' Its measurements are as follows : — 



Lines. 



Length of body 31 



Breadth of articular extremities 44 



Height of articular extremities 34 



Width of spinal canal , _ .10 



Transverse diameter of costal pits jij 



Vertical diameter of costal pits XI 



