150 
%2>i /f^n f>- l 7 ' 
1839. Ptychodus mortoni (Mantell MS.), S. G. Morton, Journ. Acad. 
Nat. Sci. Philad. vol. viii. p. 215, pi. xi. fig. 7. 
1843. Ptychodus mortoni , L. Agassiz, Poiss. Foss. vol. iii. p. 158, 
pi. xxv. figs. 1-3. 
1868. Ptychodus mortoni , J. Leidy, Proc. Acad. Nat. Sci. Philad. p. 205. 
1887. Ptychodus mortoni , A. S. Woodward, Quart. Journ. Geol. Soc. 
vol. xliii. p. 130. 
Type. Detached tooth. 
Teeth similar in form to those of the typical species of Ptychodus , 
but differing in having the centre of the crown raised into a sharp 
point, from which strong branching ridges diverge; the broad 
marginal area is marked with an almost reticulate ornament. 
The tooth from the English Chalk referred to this species % 
Dixon 1 is at present doubtfully determined. 
Form. <$f Log. Cretaceous : Alabama, U.S.A.; also Niobrara Cre¬ 
taceous of Kansas (Cope). 
28394. Tooth described and figured by Agassiz, loc. cit.; Alabama. 
Mantell Coll. 
35586-9. Four detached teeth, one being perfect and unworn, the 
others worn at the apex; Alabama. 
Presented by Prof. J. W. Mallet , 1859. 
P. 1381. Two detached teeth, one exhibiting perfectly the superficial 
coronal markings ; Alabama. Egerton Coll. 
P. 2687. Eleven detached teeth. One is of very large size, measuring 
0*05 in breadth. Alabama. Enniskillen Coll. 
Whole or fragmentary teeth of Ptychodus, from which the coronal 
layer of gano-dentine has been broken away by post-mortem abrasion, 
are sometimes discovered in the Chalk. One of these forms the type 
of Aulodus agassizi 2 , and the two following specimens are also 
figured by Dixon as “ Nascent teeth of Ptychodus .” 
28350. Abraded tooth, figured in Dixon’s Foss. Suss. pi. xxx. 
fig. 5 ; Chalk, Sussex. Dixon Coll. 
39124. Large abraded tooth, figured op. cit. pi. xxx. fig. 4; Chalk, 
Maidstone. Bowerbank Coll . 
1 Foss. Suss. pi. xxxi. figs. 6, 7. 
2 See Proc. Geol. Assoc, vol. x. (1888), p. 298. 
