M'CLUNG: THE KANSAS CRETACEOUS. 237 



which Stewart ('00, p. 273) refers to as the "supposed sple- 

 nial." This is a separate element and can be nothing but the 

 splenial. The two main divisions of the mandible are thus seen 

 to be the dentary and the dermarticular. The latter element 

 forms what might be regarded as the axis of the ramus, with 

 the dentary attached to the outer surface and the autarticular; 

 splenial and angular to the inner. The relative positions of 

 these bones, as seen in a caudal view, are represented in fig- 

 ure 4. 



PECTORAL GIRDLE OF XIPHACTINUS. 



The pectoral girdle has received considerable attention and, 

 while at first much misunderstood, is now well known in its 

 general features. Some exceptionally good material, however, 

 makes it possible for me to add to our knowledge of this portion 

 of the anatomy and to dispose of a few more unknown or prob- 

 lematical bones. Hay ('98, fig. 9) and Stewart ('99, pi. 45a, 

 figs. 1, 2) have represented major portions of the girdle. In 

 each instance, though, certain elements are omitted, and the 

 relation of the right and left halves is not shown. I think it 

 possible from the specimen before me to present a fairly com- 

 plete picture of the entire girdle. 



In figure 5 is shown a cephalic view of the two girdles 

 in position, with the horizontally directed portion of the 

 clavicle crushed and broken. Very probably this specimen 

 shows the normal relations of the two halves. The hyper- and 

 intercoracoids of the two sides are here seen to be in contact 

 throughout their dorsoventral extent, but an inspection of sep- 

 arated arches indicates that intimate union was restricted to 

 the hypocoracoids. Rising from the dorsal edges of the inter- 

 coracoids are the mesocoracoids, which define the space be- 

 tween the two arches. External to the heavy rod-shaped 

 mesocoracoids, and separated from them ventrally by an ir- 

 regular oval foramen, are the dorsal wings of the clavicles. 

 These are thickened along their cephalic edges where they are 

 in contact with the mesocoracoids, but caudally and beyond 

 this they are thin and delicate. In most specimens this part is 

 broken and gone. 



The relations of these parts as viewed from the caudal side 

 may be seen in plate X, drawn from the same specimen after 

 removal from the matrix. The separation of the mesocoracoid 

 and clavicle, except at the cephalic edge, is very evident. Here 

 may also be observed the somewhat complicated sutures be- 



