UTLIOBATID-E. 
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 1 . 
The vertebrae are very deep compared with their length, complete, 
and apparently “ cyclospondylic ” in structure. One example, from 
the Chalk of Dorking, has been described by C. Hasse 2 , under the 
name of Selache clavi[e]si. 
Ptychodus majarfiillaris, Agassiz. 
1822. Tooth allied to Diodon, G. A. Mantell, Foss. South Downs, p. 231, 
pi. xxxii. figs. 17,18, 20,21,25,27,29. 
1839. Ptychodus mammillaris , L. Agassiz, Poiss. Foss. vol. iii. p. 151, 
pi. xxv b . figs. 12-20 (P fig. 11). 
1839. Ptychodus decurrens , L. Agassiz, tom. cit . p. 154, pi. xxv. b. figs. 
3, 5. 
1839. Ptychodus altior , L. Agassiz, tom. cit. p. 155, pi. xxv. b. figs. 9, 
10 . ‘ 
1845. Ptychodus mammillaris, A. E. Reuss, Verstein. bohm. Kreide¬ 
form. pt. i. p. 2, pi. ii. figs. 11-13. 
1850. Ptychodus mammillaris , F. Dixon, Foss. Suss. p. 361, pi. xxx. 
fig. 6, pi. xxxi. fig. 4. 
1850. Ptychodus mammillaris , H. B. Geinitz, Charaet. bohm.-sachs- 
isch. Kreidegeb. 2nd edit. p. 64, pi. xvii. fig. 7. 
1850. Ptychodus decurrens , H. B. Geinitz, op. cit. p. 64, pi. xvii. 
figs. 8-12. 
1852. Ptychodus mammillaris, V. Kiprijanoff, Bull. Soe. Imp. Nat. 
Moscou, vol. xxv. pt. ii. p. 487, pi. xii. fig. 3, pi. xiii. fig. 3. 
1854. Ptychodus mammillaris , F. J. Pictet, Paleont. 2nd edit. vol. ii. 
p. 265, pi. xxxviii. fig. 27. 
1856. Ptychodus mammillaris , C. E. Fischer, Allgem. deutsch. naturh. 
Zeit. Dresden, n. s. vol. ii. p. 139, ph ii. fig. 34. 
1870. Ptychodus mammillaris , F. Roemer, Geol, von Obersclilesien, 
p. 324, pi. xxxvi. fig. 8. 
1872. Ptychodus mammillaris , H. E. Sauvage, Biblioth. Ecole Hautes 
Etudes, vol. v. art. 9, p. 16, pi. ii. figs. 86-89. 
1875. Ptychodus mammillaris, H. B. Geinitz, Palceontogr. vol. xx. pt. i. 
p. 297, pi. lxiv. fig. 26; pt. ii. p. 213, pi. xl. figs. 23-29. 
1878. Ptychodus mammillaris, A. Fritsch, Rept. u. Fiscke bohm. Kreide- 
form. p. 14, woodc. fig. 33. 
1 Science Gossip, vol. xxi. (1885), p. 109. 
2 Palaeontographica, vol. xxxi. (1884), p. 9, pi. ii. figs. 16, 17 
