1877.] 1"5 TCope 



tebrse preserved, and the surface is smooth excepting some delicate longi- 

 tudinal ridges extending to the border of the expanded extremity. The 

 narrower extremity of a dorsal vertebra is nearly round and presents ■ a 

 slight median tuberosity ; the opposite end is wider than deep, and its sur- 

 face is uniform. The smaller extremity of a lumbar vertebra is slightly 

 concave. 



Measurements. M. 



/longitudinal 023 



Diameter of dorsal centrum < vertical , 020 



' transverse 025 



Width of base of neural arch with diapophysis 010 



This species is dedicated to its discoverer, O. W. Lucas, of Canyon. City, 

 Colorado, the Superintendent of the Public Schools of the surrounding re- 

 gion. Through the scientific interest and energy of this gentleman the ex- 

 tinct vertebrata of the Dakota division of the Cretaceous Period hitherto un- 

 known to science are being brought to light. The care and skill exercised 

 by Mr. Lucas in the preservation of remains, which are often bulky, and 

 always fragile, deserve the thanks of all students of this department of 

 science. 



COMPSEMYS PLICATTJLTJS, Sp. nOV. 



Although tortoises have been discovered in older formations in Europe, 

 the present species is the earliest yet obtained in North America. Its 

 characters appear to coincide in important respects with those of the Lig- 

 nitic formation which I have referred to Compsemys Leidy. This name I 

 have proposed to retain for tortoises with marginal bones completely 

 united with solid plastron, and the usual dermal scuta, and which differ from 

 Emys in their Trionyx-like sculpture. 



The 0. plicalulus is represented by portions of both carapace and plas- 

 tron of several individuals. While the distal extremities of the costal bones 

 display the suture for the marginals, they also possess an inferior true costal 

 prolongation, as in Trionyx. The proximal part is not preserved in any 

 marginal bone, but the adjacent portions were united by fine suture. The 

 proximal extremity of the costals exhibit the usual two directions, the 

 shorter being posterior, and relating to the anterior part, of the succeeding 

 vertebral bone. The sternal sutures are fine ; that between the hyo- and 

 hyposternal bone is transvere ; while that between the latter and the post- 

 abdominal is oblique, and at the margin quite squamosal. At that point 

 the hyosternal underlaps the post-abdominal for a considerable distance, 

 and the suture of the inferior side of the plastron, after bending forwards, 

 is abruptly recurved, running along the edge of the posterior lobe. 



The scutal sutures are not wide nor deeply impressed, but the abdomino- 

 femoral, and the femoro-anal are distinct. The median, longitudinal, sternal, 

 and the costo-marginal sutures are irregular and serpentine. The sculp- 

 ture is rather fine, and consists of rather closely placed tubercles and ridges. 

 The borders of the elements of both carapace and plastron are marked 



