138 
SELACHII. 
Ptychodus oweni, Dixon. 
1850. Ptychodus oiueni, F. Dixon. Foss. Suss. p. 364, pi. xxxi. fig. 2. 
Type. Detached tooth ; British Museum. 
Teeth with rounded, moderately elevated crowns, ornamented 
with widely separated ridges, which rarely extend directly from side 
to side, but are disposed in an irregular manner; the marginal 
finely marked area is insignificant. 
This species is very imperfectly known and appears to be rare. 
Form. Log. Senonian : S.E. England. 
39125, 39125 a. Type specimen and four associated teeth; Upper 
Chalk, Snodland, Kent. One of the teeth, shown in PI. V. 
fig. 8, evidently represents the lower median row; a few 
of the transverse ridges upon the crown are continuous, 
regular, and parallel in the middle, but those placed pos¬ 
teriorly are very irregular and discontinuous. 
Bowerbank Coll. 
39700. Abraded and worn tooth, supposed lower median; Kent. 
Purchased , 1866. 
P. 2688. Similar tooth ; Sussex. Enniskillen Coll. 
28342. Typical tooth ; Lewes, Sussex. Dixon Coll. 
Ptychodus decurrens, Agassiz. 
1752. Dens piscis Ostracionis, F. E. Briickmann, Acta Phys. Med 
vol. ix. p. 116, pi. v. fig. 4. 
1811. Palate of Unknown Fish, J. Parkinson, Organic Remains, vol. iii. 
pi. xviii. fig. 12. 
1839. Ptychodus decurrens, L. Agassiz, Poiss. Foss. vol. iii. p. 154, 
pi, xxv. h. figs. 1, 2, 4, 6-8 ( non figs. 3, 5). 
1840-45. Ptychodus decurrens, R. Owen, Odontography, vol. ii. pis. xviii., 
xix. 
1850. Ptychodus decurrens , F. Dixon, Foss. Suss. p. 362, pi. xxx. 
figs. 7, 8, pi. xxxi. fig. 1, pi. xxxii. fig. 5. 
1850. Ptychodus depressus, F. Dixon, op. cit. p. 363, pi. xxxi. fig. 9. 
1852. Ptychodus decurrens, P. Gervais, Zool. et Pal. Fran^. pi. lxxviii. 
1852. Ptychodus decurrens , V. Kiprijanoff, Bull. Soc. Imp. Nat. Moscou, 
vol. xxv. pt. ii. p. 490, pi. xiii. figs. 4 \ 5. 
1852. Ptychodus decurrens, F. A. Quenstedt, Handb. Petrefakt. p. 181, 
pi. xiii. fig. 59. 
1 The original of this figure is a doubtful tooth subsequently assigned to 
P. oiveni (Y. Kiprijanoff, toe. cit. 1881, pt. ii. p. 2). 
