The remains of ammonites recovered from these beds by the
boring are very unsatisfactorily preserved and are so fragmentary
that their identification is a matter of great difficulty. Some of
the forms of Perisphinctes show marked " polyplocoid " degenera-
tion. Thus, a specimen from between 738 feet and 755 feet in
depth, referred by Mr. Buckman provisionally to P. discobolus ,
possesses a distinctive ornamentation of unevenly spaced primary
ribs, some of which are stronger than others, dividing at about
the middle of the flank, or a little externally to this, into groups
of from two to four secondary ribs. Intercalary secondary ribs
also occur. The specimen has suffered from crushing, so that the
flatness of the relatively extensive flank may have become some-
wjhat emphasised. Yet the original whorl-section would be likely
to show little more rotundity since the umbilical marginal slope
has suffered in no marked degree but is still well indicated.
1 P. de Loriol and G. Cotteau. 'Monographie paleont. et geol. de l'e'tage
Portlandien du depart, de 1' Tonne,' Bull. Soc. Set. Hist, et Nat. de FYonne,
ser. 2, tome i , 1868, p. 189, pi. xii., fig. 8.
