Stewart.] Cretaceous Fishes. 259 



TELEOSTEI. 



The fishes belonging to this order are usually characterized 

 by the margin of the upper jaw being formed of the maxilla 

 and premaxilla and by the absence of spinous rays in the pelvic 

 fin. Some of the Cretaceous forms are exceptions to this, as 

 the pelvic fin often is provided with spinous rays. The parietal 

 bones are united in the median line and the scales are usually 

 cycloid. This order comprises the most generalized types of 

 bony fishes, which are closely related to the bony ganoids. 

 They are among the most abundant fossils obtained- from the 

 chalk of western Kansas, and are usually in an excellent state 

 of preservation, which makes them easy to collect and study. 

 They range in size from the gigantic Xiphactinus, which often 

 attains a length of nearly twenty feet, to Enchodus and some 

 of the other small forms, which are often less than a foot in 

 length. They are found most abundantly in the Niobrara group, 

 not because they were more abundant in that period, but prob- 

 ably because the conditions which prevailed at that time were 

 more favorable for fossilization than in the Fort Pierre and Fox- 

 Hill time which followed. They include several families, which 

 will be described and discussed below. 



A. S. Woodward, 14 of the British Museum, has divided 

 these fishes into six groups, which are given below. 



"I. Laterally compressed fishes with large and powerful maxilla 1 and pre- 

 maxilhe, bearing teeth, the dentary being the only tooth-bearing bone of the lower 

 jaw. provided with a single scries, the palatine and ectopterygoid toothless. The 

 tee th are placed in complete sockets. Vertebra", except near the head, deeply 

 two-grooved on each side in addition to possessing pits for insertion of neural and 

 haemal arches. Ex.: Portheus I Xiphactinus), TchthyodecteSt Daptinus (Sau- 

 rodon . Saurocephalus | forming the family of Saurodontidaz of Cope). 



••II. Fishes somewhat less laterally compressed, provided with scales or bony 

 scutes, or both, and having the premaxilla- and maxilla* large, bearing powerful 

 fceetfa in one or more series. The teeth not implanted in sockets, but anchylosed 



14. Pn.c QeoL Assoc., vol. X, 1888, pp. 809, 810. 



