AMMONITES AND NAUTILOIDS OF WADI HAJAR 



45 



diameter. The holotype of P. cocosifonne Spath ( 1931 ; pi. 115, fig. 

 1 ; received by Spath after his main de.scription of Paryphoceras) is 

 also strikingly like the Yemeni specimens, but differs slightly in the 

 presence of about six single ribs amongst the 35 primary ribs on its 

 outer whorl. These Cutch specimens occur in the Middle and Upper 

 Oxfordian (Transversarium and Bimammatum Zones). 



Occurrence. Base of the Billum Member, Naifa Formation, 

 Jebel Billum andAl Ma'abir; Bimammatum Zone, Upper Oxfordian. 



Ammonites in the Madbi Formation 



Poorly preserved ammonites occur in all three Storm Beds in the 

 Madbi Formation. They are rare in the Middle Storm Bed, from 

 which only three very poor fragments were obtained; two, 

 CA 1286-87, are indeterminate Ferisphinctids, but the third, 

 CA1183 (PI. 7, fig. 3). is probably a Peltoceratoides, indicating a 

 Lower Oxfordian age. Ammonites are found somewhat more com- 

 monly in the Upper Storm Bed, and eight fragments, CA 1288-95, 

 were obtained in sizes of up to 45 mm whorl height; several have 

 the quadrate whorl section and straight primary ribs bifurcating at 

 the ventro-lateral edge characteristic of Perisphinctes s.s. (PI. 5, 

 fig. 3). They could well belong species from the Plicatilis to 

 Bifurcatus Zones of the Middle and Upper Oxfordian. All came 

 from the outcrop 1 km east of the road, south of the river crossing 

 at Al Ma'abir. A small Laevaptychus (CA839, from an 

 Aspidoceratid), was obtained from the Lower Storm Bed in the 

 Madbi Formation in central Jebel Billum. This meagre evidence 

 suggests that the Madbi Formation is of approximately Lower, 

 Middle and possibly basal Upper Oxfordian age. 



Superfamily PERISPHINCTACEAE Steinmann, 1890, p. 441 



Family PERISPHINCTIDAE Steinmann, 1890 



Subfamily PERISPHINCTINAE Steinmann, 1890 



Remarks. Torquatisphinctes - Pachysphinctes - Katwliceras is 

 one of the last lineages of this subfamily, which takes it into the 

 Hybonotum Zone, Lower Tithonian. The work of Callomon (1981: 

 123, 149), Verma & Westermann (1984: 37-47) and Krishna & 

 Pathak (1993: 229) suggests that this is a well-documented lineage 

 of Tethyan Perisphinctinae, which is distinct from the more involute, 

 tabulate and interrupted venters of most Idoceratinae, and from the 

 virgatotome ribbing of the Ataxioceratidae (including the 

 Virgatosphinctinae). 



Genus LARCHERIA Tintant, 1961 



Type species. Larcheria larcheh Tintant, 1961. 



Remarks. The genus Larcheria consists of the more involute, 

 discoidal and multiplicate Ferisphinctids that appear in the upper 

 half of the Middle Oxfordian Transversarium Zone. L. larcheri, L. 

 schilli (Oppel) and their allies are confined to that horizon in 

 southern Europe (Atrops & Melendez, 1993; Melendez & Fontana, 

 1992), but L. gredingensis (Wegele, 1929) and L. domi Tintant 

 (1961: 137) are found in the Upper Oxfordian Bimammatum Zone 

 in the Franconian Alb, associated with Orthosphinctes polygyratus 

 (Reinecke) (Cariou & Hantzpergue, 1997: 85). The Yemeni speci- 

 mens are identified with this younger group of species of 

 Larcheria. 



Larcheria gredingensis (Wegele, 1929) PI. 3. figs 4, 5 



1929 Perisphinctes gredingensis Wegele: 49, pi. 1. fig. 7. 



Material. Four specimens: three, CA823-25. 7-8 m above the 

 base of the Billum Member at the Perisphincfid Cliff near the eastern 

 end of Jebel Billum (additionally a photograph of another specimen 

 was taken in the field ); and CA 1 088 from the basal part of the Billum 

 Member about 1 km east of the Al Ma'abir road/river crossing. 



Description. All are crushed fiat laterally, three being about 1 20 

 mm diameter, the fourth (from the Al Ma'abir locality) is 80 mm 

 diameter. The whorls are slightly involute, and the whorl section 

 appears to have been compressed originally. Long, straight, 

 prorsiradiate primary ribs bifurcate or trifurcate on the outer half of 

 the whorl, and they do not diminish in strength up to the largest sizes 

 seen. The ratio secondaries/primaries is 2.5-2.7/1 . 



Remarks. These ammonites are more involute and have finer ribs 

 than Orthosphinctes polyplocus with which they occur. One of the 

 figured specimens (PI. 3, fig. 4) is a very close match for Wegele's 

 (1929: pi. 1, fig. 7) holotype from the Bimammatum Zone in 

 Franconia, southern Germany. Another species from the same hori- 

 zon in Franconia is i. </onn' Tintant ( 1 96 1 : \37: nam. nor. forDorn, 

 1930: 144, pi. 7. fig. 5), which is more involute and more densely 

 ribbed than L. gredingensis. 



Occurrence. Lowest 5-8 m of the Billum Member, Naifa For- 

 mation, Jebel Billum and Al Ma'abir; Bimammatum Zone, Upper 

 Oxfordian. 



Genus ORTHOSPHINCTES Schindewolf, 1925 



Type species. Ammonites tiziani Oppel, 1863 (=Nautilus 

 polygyratus Reinecke, 1818). 



Remarks. Atrops (1982: Al -62) used the ?.\ihgen\i?.Orthosphinctes 

 (Orthosphinctes) for microconchs corresponding to the macroconch 

 subgenus O. (Lithacosphinctes). They occur in the Bimammatum, 

 Planula and base of the Platynota Zones, and follow the last of the 

 many forms of Perisphinctes and its subgenera in theTransversarium 

 and Bifurcatum Zones. The sequence of species was refined in the 

 synthesis of Atrops & Melendez (1993: 22-26): Orthosphinctes 

 polygyratus first occurs in the Bimammatum Zone (Bimammatum 

 Subzone), where it is associated with Larcheria gredingensis 

 (Wegele), then it occurs again in the bottom subzone of the Platynota 

 Zone at the base of the Lower Kimmeridgian (Cariou & Hantzpergue, 

 1997: 85. 89). 



The Yemeni examples of Orthosphinctes are not well-preserved 

 and dimorphs cannot be identified (though at 250 mm or more in 

 diameter some are almost certainly fragments of macroconchs), but 

 their presence confirms the Bimammatum Zone date at the bottom of 

 the Billum Member that is indicated by Larcheria. Euaspidoceras and 

 the Mayaitids Epimayaites and Paryphoceras at the same horizon. 



Orthosphinctes polygyratus (Reinecke, 1818) 



PI. 3, figs 7, 8 



1818 Nautilus polygyratus Reinecke: 73, pi. 5, figs 45, 46. 



1863 Ammonites tiziani O^^eV. lAb. 



1 877 Ammonites (Perisphinctes) polygyratus (Reinecke); Loriol: 



61,pl. 7, fig.l. 

 1929 Perisphinctes tiziani (Oppel); Wegele: 44, pi. 1, figs 4, 5. 

 1935 Planites aff. polygyratus (Reinecke); Spath: 209, pi. 25, fig. 



5. 

 1961 Perisphinctes (Orthosphinctes) polygyratus (Reinecke); 



Geyer: 21, pi. l,fig. 4. 

 1961 Perisphinctes (Orthosphinctes) tiziani (Oppel): Geyer: 19, 



pi. 1, fig. 2; pi. 2, fig. l;pl. 6. fig. 3. 



