334 KANSAS UNIVERSITY SCIENCE BULLETIN. 



premaxillse are canine in form, those at the posterior being 

 small and rounded. There are six to eight of the sharp teeth 

 on the mandibles and about the same number on the two pre- 

 maxillse. The teeth are not placed in sockets, but, on the con- 

 trary, are hollow and are placed on cones. These cones are 

 ridged in a neat pattern, and the base of the tooth corresponds 

 to it, helping to hold the tooth firm. 



The canine-shaped teeth are the most firmly anchored, as 

 they would have the most strain on them. They are hollow for 

 about one-fourth of their length and the cone is correspond- 

 ingly lengthened. The heavy molars are only slightly concave 

 at the base, but to offset this the cone is very deeply ridged 

 and thus holds the tooth firm. Even after maceration most 

 of them will be found in position. 



Minute Structure. (See plate XXVIII, figs. 7, 8.) 



The structure is quite complex for a fish tooth, there being 

 thin layers of enamel and dentine. A longisection (see 

 plate XXIX, fig. 9) shows many canals radiating toward the 

 periphery. The canals start from a cavity at the apex of the 

 concavity of the base, and all extend upwards and outwards 

 toward the periphery, where they branch out, forming a net- 

 work under the enamel. A transverse section (plate XXIX, 

 fig. 10) shows the canals in cross-section, and also a longisec- 

 tion of some of them where they are curving outward to the 

 periphery. The teeth do not show any striations under the 

 lens, but are smooth and polished on the sides, the upper por- 

 tion being roughened by use. The sides are ridged near the 

 base and correspond to the outline of the cone on which they 

 are placed. The pattern of the cone is so marked that it is 

 easy to replace the teeth on the right cones, even after they are 

 removed and misplaced. (See plate XXVIII, fig. 8.) 



DETAILED DESCRIPTION OF THE INDIVIDUAL BONES OF 



THE SKULL. 



The skull is made up of the following bones and they are 

 described in this order: 



1. Supraoccipital. 7. Parietal. 13. Prefrontal. 



2. Exoccipital. 8. Pterotic. 14. Ethmoid. 



3. Basioccipital. 9. Sphenotic. 15. Vomer. 



4. Epiotic. 10. Alisphenoid. 16. Suborbitals. 



5. Prootic. 11. Parasphenoid. 17. Hyomandibular. 



6. Opisthotic. 12. Frontal. 18. Metapterygoid. 



