IN THE ANGLO-PARIS BASIN 121 



distribution of Beudanticeras laevigatum, B. sanctaecrucis and B. albensis is not 

 affected by either of these two factors. In fact the lyelli Subzone may be recognised 

 in areas in which sea-bottom conditions produced a sulphide facies in the sediments, 

 by the association of Hoplites (H.) spp. and these three species of Beudanticeras. The 

 distribution of Douvilleiceras is also not constant. It is rare at Small Dole, although 

 very common at the top of the lyelli Subzone at Courcelles. It was also not un- 

 common in Bed 14 at Shere (Owen 1963a ; 42). 



The uppermost part of the lyelli Subzone and its junction with the overlying spathi 

 Subzone cannot alone be determined by the abrupt disappearance of Lyelliceras lyelli. 

 In England, at Small Dole, Sevenoaks (p. 23), and Westerham (p. 31), and at Courcel- 

 les (Aube), there are clays just below the spathi Subzone which still contain lyelli 

 Subzone species of Beudanticeras, Douvilleiceras (Courcelles only), and Protanisoceras 

 (P.), but Lyelliceras is absent. It is recommended that these sediments be included 

 in the lyelli Subzone for the significant change in the ammonite fauna occurs at the 

 top of them where all the non-Hoplites {H.), lyelli Subzone ammonite species vanish 

 abruptly from the sequence. In the English and French sections mentioned here 

 there is no apparent break in deposition and no change in facies. Protanisoceras (P.) 

 still occurs in the spathi Subzone but it is very rare, and, in effect, the heteromorphs 

 are almost exclusively species of Hamites (H.) with subordinate Metahamites. There 

 is no major change in the species of Hoplites (H.) in the transitional period between 

 the lyelli and spathi Subzones. The transitional sediments at the top and bottom 

 of the lyelli Subzone are of no great thickness in well developed sequences. Even 

 slight condensation produces an apparent sharp change in the ammonite fauna at the 

 subzonal boundaries. 



(c) Subzone of Hoplites (Hoplites) spathi 



H. (H.) spathi in its typical form occurs in this subzone but it is not very common, 

 although there is no dearth of closely related forms. It is possible that Spath 

 selected this species (1941 ; 668 : 1942 ; 672, under the preoccupied name bonarellii) 

 because in terms of ornament it stands mid-way between the more discoidal finer 

 ribbed species of the dentatus type and the inflated coarsely ornamented forms of the 

 maritimus-rudis group. The name dentatus-spathi Subzone is in any case too well 

 established in the recent literature both sides of the Channel to justify altering it, 

 except to reduce it to a single index of H. (H.) spathi. 



The Subzone is well developed in England and the section at Small Dole is par- 

 ticularly important as it shows in a very fossiliferous little condensed sequence the 

 junction with the lyelli Subzone below and, albeit imperfectly, the intermedius Sub- 

 zone above. In France, the junction with the lyelli Subzone is seen in an uncon- 

 densed sequence at Courcelles, and the junction with the intermedius Subzone again 

 in an uncondensed sequence at Revigny-sur-Ornain (p. 88). The ammonite fauna 

 consists very largely of species of Hoplites (H.) of which the general evolutionary 

 characteristics of stratigraphical value have been given by me (Owen 1963a ; 49). 

 The very small percentage minority element in the fauna provides a good list of 

 genera and species (p. 152) some of which are of value in correlation with other faunal 

 provinces. 



