279 



The abutments of the neural arch are firmly co-osified with the body, but 

 their sutural connection is plainly visible. Just below the suture, the side of 

 the body presents a concavity. The beginning of. a groove or narrow con- 

 cavity is .also seen extending forward beneath the body. The lateral surfaces 

 of the specimen are smooth, excepting near the everted articular border of 

 the body, where they are roughened for the firmer attachment of ligaments. 



Poicilopleuron was probably a semi-aquatic Dinosaurian, an animal equally 

 capable of living on land or in water, and perhaps spending most of its time 

 on shores or in marshes. Whether the cavernous structure of its skeleton 

 was related to pneumatic functions, as in birds, flying reptiles, and some 

 others, or whether it was only occupied with ordinary marrow, is a question 

 that appears uncertain while our knowledge of the skeleton itself is so 

 incomplete. 



Order Chelonia. 



Among Dr. Sternberg's collection of fossils from the Smoky Hill River, 

 Kansas, there are several which appear to be the limb-bones of a turtle. 

 Similar bones from the Cretaceous formation of New Jersey and Mississippi 

 I formerly attributed to species of Mosasaurus, but the recent discoveries of 

 characteristic portions of the skeleton of this and allied animals, retaining 

 the limbs, have proved that view to be erroneous. 



A huge turtle, represented by the proximal extremity of a humerus found 

 in the green sand of^ew Jersey, was named by Professor Agassiz Atlan- 

 tochelys*Mortoni. Professor Cope has described some remains of a species 

 nearly as large as the former, from Kansas, under the name of Protostega 

 gigas; and an arm-bone of a smaller turtle, from the Cretaceous formation 

 of Mississippi, he has referred to a species with the name of P. tuberosa. 

 Remains of a turtle,, about the size of the Mississippi snapper, from Kansas, 

 he has attributed to another genus with the name of Cynocercus incisus. The 

 specimens of limb-bones above mentioned, and represented in Figs. 17 to 21, 

 Plate XXXVI, are not large enough to pertain to the smallest of the three 

 species of Atlantochelys indicated, but would sufficiently relate in size with 

 the remains of Cynocercus incisus to belong to that animal. 



The bones appear unusually flat, but this condition, in part at least, is due 

 to compression. 



Fig. 17, Plate XXXVI, represents the upper extremity of a humerus 



