(2 COLORADO COLLEGE STUDIES. 



Mesodon abrasus, sp. nov. 



Plate II, figs. 18 and 20. 



Tliis unme is proposed for certain pycnodoiit teeth of low. 

 rlioiuboidal form and feebly convex upper surface which 

 occur in No. 8 of the "Belvidere section," southwest of the 

 Belvidere railway station, and seem to agree with the larger 

 mandibular teeth of Me»o(ion. The specific name refers to 

 the occurrence in the tyi)e-specimen (see fig. 18) of two small 

 oblique facets produced at one end by attrition. 



Measurements. — The type has a height (above root) of 3, 

 a length of 13, and a breadth of 6 mm. 



To the vomerine set of the same species may belong the 

 rotund-oval, or nearly hemispherical teeth of similar height 

 but smaller size which occur not uncommonly at the same 

 locality and horizon, the largest now available example of 

 which (see figs. 15-17) measures about H and 7 mm. in minor 

 and major horizontal diameters. 



( ?Lamna) quinquelateralis, sp. nov. 



Plate II, figs. 9 aud 10. 



The specific name, quinqiieldteralis, is applied to a species 

 of shark whose vertebme differ from all others of which I have 

 any knowledge. The type- vertebra is short, much broader 

 than high, shallow-cupped, and more or less sharply pentago- 

 nal ended. 



Measurements. — Height 20, length 12, breadth 28 mm. 

 The two upper angles measure each about 130 degrees; either 

 lateral angle about 105 degrees. The lower angle is broad 

 and rounded. 



Occurrence. — A single vertebra of this form was found by 

 the writer at Belvidere, Kansas, with the above-described 

 remains of Plesiochelys, in the upper part of No. 4 of the 

 " Belvidere section." 



Hybodus clarkensis, sp. nov. 



Plate II, figs. 11-14. 



Fill-spine large, gently recurved, laterally compressed, the 

 sides being nearly flat, the anterior border subacute, or form- 

 ing a sort of keel, the posterior part beveled on either side 



