NATURAL SCIENCES OF PHILADELPHIA. 207 



fore and aft, and has perhaps been about 8 lines high. The summit is worn ofiF, 

 leaving an exposed flat circular surface of vaso-dentine half an inch in diame- 

 ter. The root is 15 lines wide, 6 lines fore and aft, and three lines thick. The 

 smaller specimen consists of an unworn crown 11 J lines wide, 7 lines fore 

 and aft and 5^ lines high. 



Ptychodus occidentalis, n. s. 



The Museum of the Academy contains a specimen consisting of the crown 

 of a tooth of a species oi Ptychodus differing from any other previously known. 

 It was obtained by Dr. John L. LeConte, in association with other remains of 

 fishes, from an ash-colored rock of the Cretaceous series, a few miles east of 

 Fort Hays, Kansas. 



The tooth is remarkable, especially from the comparatively near approxima- 

 tion of its diameters, the width transversely and fore and aft and the height 

 approaching one another more nearly than in any other species. The fore- 

 part of the crown is somewhat injured and the root is broken away. The 

 transverse diameter of the crown at base is 14 lines ; the fore and aft diameter 

 has been about an inch ; and the height is also an inch. 



In shape the crown is a blunt cone with the sides sloping evenly to the base 

 and to the posterior sinus. The latter is a triangular concavity about two- 

 thirds of the breadth in height. 



The direction and arrangement of the ridges of the crown are much like as in 

 the European Ptychodus decurrens, but the principal ridges crossing the crown 

 transversely are finer and the intervals much narrower, indeed the space occu- 

 pied by a pair of ridges with their interval in /'. decurrens would accommodate 

 three ridges with a pair of intervals in P. occidentalis. Descending the sides of 

 the cone the ridges branch as in /'. Mortoni, and at the basal half of the crown 

 form a reticulation much as in P. decurrens. At the back of the summit of the 

 crown the principal ridges continue their transverse or parallel course until 

 near the upper part of the. sinus, into which as they descend thej- are resolved 

 into a fine reticulation. The fore-part of the crown is occupied by a reticula- 

 tion formed by the descent, convergence and division of the more anterior 

 principal ridges. 



From the description it will be observed that the tooth holds an interme- 

 diate position in anatomical character to those of Ptychodus Mortoni, and 

 P. decurrens. 



Three small teeth, found by Dr. Le Conte in association with the latter, re- 

 semble, in their proportions and in the proportionate size and arrangement of 

 the ridges of the crown, the teeth of P. decurrens, but perhaps may belong to 

 the same species as the large tooth above described. The larger of the three 

 specimens is perfect, but has the summit of its crown worn ott'. The crown 

 measures 7 lines transversely, 6 lines fore and aft, and has been from 4 to 5 

 lines high. The root is 6 lines wide, 4^ lines fore and aft, and 2\ lines thick. 

 Comparatively coarse ridges cross the crown transverselj^, curving forward 

 laterally and ending in a marginal reticulation. Branching ridges descend in 

 front from the foremost of the transverse ridges, and likewise end in a marginal 

 reticulation. The sinus is occupied by a finer reticulation joined by fine ridges 

 descending from the summit and sides of the crown. The smallest tooth, like- 

 wise perfect, has the crown 4^ lines wide, 3| lines fore and aft, and 2^ lines 

 high. 



Three additional specimens associated with the former ones, are the smallest 

 teeth of Ptychodus I have seen, but I suspect that they belong to the same 

 species. They are transversely ellipsoidal in outline at the base of the crown, 

 and this appears as a low cone elevated at the inner third and with a broad 

 expanding base. The sinus is situated at the inner posterior third. The sur- 

 face of the crown is crossed with transverse ridges which form a narrow retic- 

 ulation at the border. The largest of these small specimens is 3^ lines trans- 

 versely, 1| fore and aft, and | of a line high from the root. The smallest tooth 

 is 2\ lines wide, 1^- fore and aft, and ^ a line from the root. 



1868.] 



