JITLIOBATID.i;. 
133 
In the one jaw, presumably the lower (fig. 6, B), the median 
series of teeth is the largest, and the lateral rows are arranged 
symmetrically, diminishing in size to the left and right. In the 
opposing dentition (fig. 6, A), the median series is very small, 
and the first lateral row on each side large, with the outer lateral 
series successively diminishing in size’. 
The vertebrsB are very deep compared with their length, complete, 
and apparently “ cyclospondylic ” in strncture. One example, from 
the Chalk of Dorking, has been described by C, Hasse^, under the 
name of SelarJu 
Ptychodus mammillaris, Agassiz. 
1822. Tooth allied to Diodon, G. A. Mantell, Foas. South Downs, p. 231, 
pi. X.X.VU. figs. 17, 18, 20, 21, 25, 27, 29. 
1839. Ptychodm mammillarii, L. Agassiz, Poiss. Foss. vol. iii. p. 151, 
pi. XXV b. figs. 12-20 (? fig. 11). 
1839. Ptychodm dcmrrem, L. Agassiz, tom. cit. p. 154, pi. xxv. h. figa 
3, 5. 
1839. Ptychodm altior, L. .Agassiz, tom. cit. p. 155, pi. xxv. b. figs. 9, 
10 . 
1845. Ptychodm mammillaris, A. E. Reuss, Verstein. bohm. Kreide- 
form. pt. i. p. 2, pi. ii. figs. 11-13. 
1850. Ptychodm mammillaris, F. Dixon, Foss. Suss. p. 361, pi. xxx. 
fig. 6, pi. xxxi. fig. 4. 
1850. Ptychodm mammillaris, II. B. Geinitz, Charact. bohm.-sachs- 
isch. Kreidegeb. 2nd edit. p. 64, pi. xvii. fig. 7. 
18.50. Ptychodus decurrens, II. B. Geinitz, op. cit. p. 64, pi. xvii. 
fig.a 8-12. 
1852. Ptychodm mammillaris, V. Kiprijanoff, Bull. Soc. Imp. Nat. 
Moscon, vol. xxv. pt. ii. p. 487, pi. xii. fig. .3, pi. xiiL fig. 3. 
18*54. Ptychodm tnammillaris, F. J. Pictet, Pal^ont. 2nd edit. vol. ii. 
p. 265, pL xxxviii. fig. 27. 
1856. Ptychodm mammillaris, C. E. Fischer, Allgem. deutsch. naturh. 
Zeit. Dresden, n. s. vol. ii. p. 139, pL ii. fig. 34. 
1870. Ptychodm mammillaris, F, Roemer, Geol. von Oberschlesien, 
p. 324, pi. xxxvi. fig. 8. 
1872. Ptychodus ynammillaris, II. E. Sauvage, Biblioth. Ecole Ilautes 
Etudes, voL v. art. 9, p. 16, pL ii. figs. 86-^9. 
1875. Ptychodm mammillaris, H. B. Geinitz, Palaeontogr. vol. xx. pt. i. 
p. 297, pi. btiv. fig. 26 ; pt. ii. p. 213, pi. xl. figs. 23-29. 
1878. Ptychodus mammillaris,X. Fritsch, Rept. u. Fische bohm. Kreide- 
form. p. 14, woodc. fig. 33. 
' Science Gossip, vol. xii. (1885), p. 109. 
“ Palaeontographica, vol. xxxi. (1884), p. 9, pi. ii. figs. 16, 17 
