164 



I'ROCEEDINQS OF THE NATIONAL MUSEUM. 



VOL. XXXII. 



A NOTE ON THE GENUS CAMPTOSAURUS. 



Fig. 8.— Ventr.-vl view of at- 

 las AND AXIS OF CAMPTO- 

 SAURUS (Cat. No. 5473), i NAT. 

 SIZE. .1^ In., Atlas inter- 

 centrum; Ax., axis; Ax. III., 

 axis intercentrum; r., fa- 

 cets FOR RIBS. 



In coiupariug- the axis of Morosaurus agills with the homologous 

 parts of other Dinosaurian specimens in the U. S. National Museum, 

 the writer found, on the axes of two individ- 

 uals of "the genus Camptosauru>i., intercentra 

 attached by suture to the centra of the axes. 

 So far as the writer is aware, this element has 

 not been observed before in a representative 

 of the Orthopoda. In the smaller (No. 5474, 

 U.S.N.M.) and probably younger specimen 

 the intercentrum has been somewhat crushed 

 out of position, but in the larger specimen (No. 

 5473, LT.S.N.M.) it is retained in place, as 

 shown in fig. 8 {Ax. In.). 



Inferiorly the intercentrum of Cdinptoscmrus 

 is roughly subelliptical in form, the longer 

 axis being transverse. It is closely united b}^ 

 suture to the lower half of the anterior end of 

 the centrum, forming a prominent liplike pro- 

 jection which, when articulated, underlaps 

 somewhat the intercentrum of the atlas. In a fully adult specimen this 

 element would probably become co-ossified, as in MorosanriLS grandis, 

 and thus lose its identit}'. Viewed from 

 the side, it is triangular in form, the deepest 

 portion being next to the centrum. The 

 inferior surface is gently convex trans- 

 versely and slightly concave antero-pos- 

 teriorly. Seen from the front, the center 

 has the greatest vertical depth, the upper 

 margins gradually sloping down to the lat- 

 eral borders. The anterior face is smooth 

 and somewhat concave supero-inferiorl3^ 

 There are two small pits on the median 

 anterior part of the inferior surface. The 

 presence of an axis intercentrum in both 

 the Opisthoc(jelia (Sauropoda) and Orthopoda 

 (Predontata) tends to confirm somewhat the 

 contention of Marsh and Hatcher that the 

 Dinosauria is a natural group, and in the ex- 

 amples cited here it should l)e considered a persistent primitive char- 

 acter which was present in a remote but common ancestor. 



Fig. 9.— Ischia of Morosaurus; 



INFERIOR VIEW, j'g NAT. SIZE. 6., 



Distal ends; il., face for ilium; 



p., DISTAL extremity; ph., FACE 



for pubis; s., symphysis. 



