AMMONITES AND NAUTILOIDS OF WADI HAJAR 



39 



Fig. 1 Steblites plicodisciis (Waagen). on limestone pavement formed by 

 top bed of Billum Member (fauna 6). below west cliff. Wadi Arus; xl.l 

 (from a colour photograph taken in the field). 



some. The whorls arc involute oxycones, with an angled or bluntly 

 rounded venter. At sizes of 50-100 mm diameter the whorl height is 

 52-56% of the diameter and the umbilical width is 11%. Feeble 

 falcoid ribs or striae can be seen crossing parts of the side of the 

 whorl, though they are very weak in the middle part of the whorl side 

 and more prominent near the venter. 



Remarks. Waagen's sole original specimen was only 31 mm 

 diameter, but Spath re-interpreted the species from more than 20 

 larger well-preserved specimens, which he claimed showed the 

 complete range from small 'smooth young to smooth adult" (Spath, 

 1928: 148), some of which were still septate at 1 10 mm diameter. 

 The ribs are always feeble except for the forwardly inclined cres- 

 cents at the ventral edge. The amount of variation in rib strength is 

 not clear from either the original Cutch or the present Yemen 

 specimens, so it is not clear whether Strehlites habyensis Spath 

 ( 1 928: 1 5 1 , pi. 8 fig. 1 ) with its slightly stronger ribs is a synonym, 

 though the nearly smooth species S. leptodiscus Spath (1928: 150, 

 pi. 16, fig. 1) does not appear to be different. Their age in Cutch is 

 Eudoxus and Beckeri Zones. Specimens that almost certainly be- 

 long to the same species were described by Verma & Westermann 

 (1984) from the Hybonotum Zone at Mombasa, and several speci- 

 mens from the same Eudoxus to Hybonotum Zone age range were 

 described by Collignon ( 1959) from Madagascar. 



Occurrence. Top bed of the Billum Member, Naifa Formation, 

 west cliff of Wadi Arus; Eudoxus or Beckeri Zones, Upper 

 Kimmeridgian. 



aptychi of the family Oppeliidae. they are probably from Tara- 

 melliceras, species of which occur in both parts of the Kilya Member 

 from which the aptychi have been obtained. 



Occurrence. Lower and middle parts of the Kilya Member, 

 Naifa Formation, Naifa Cliff and Wadi Kilya; Beckeri Zone. Upper 

 Kimmeridgian. 



Subfamily STREBLITINAE Spath, 1925 

 Genus STREBLITES Hyatt, 1900 



Type SPECIES. Ammonites tenuilobatus Oppe\. 1862. 



Strehlites plicodiscus (Waagen, 1875) 



Fig. 1 



1875 Oppelia plicodiscus Waagen: 56, pi. 10, fig. 5. 



1928 Steblites plicodiscus (Waagen); Spath: 148, pi. 16. fig. 2; pi. 



17, fig. 1. 

 1928 Streblites leptodiscus Spath: 150, pi. 16, fig. 1. 

 1959 Steblites plicodiscus (Waagen); Collignon: pi. Ill, figs 



409,410. 

 1959 Steblites habyensis Spath; Collignon: pi. 1 1 1 , fig. 41 1 . 

 1984 Steblites habyensis Spath; Verma & Westermann: 36, pi. 3, 



fig. 3. 



Material. Many specimens can be seen on the limestone pave- 

 ment formed by the top 1 m thick bed of the Billum Member, below 

 the cliff with microbialite boulders on the west side of Wadi Arus; 

 photographs were taken of four specimens in the field. 



Description. All specimens are crushed flat on the bedding 

 plane, though slight relief and the curvature of the side of the whorl 

 is retained in the body-chamber of some examples. Specimens of up 

 to 125 mm diameter were seen, several with about 0.6 whorls of 

 body-chamber and parts of the final mouth-border. The highly 

 complex suture-line is visible at the end of the phragmocone in 



Genus UHLIGITES Kilian, 1913 



Type species. Streblites kraffti Uhlig, 1903, subsequently desig- 

 nated by Roman (1938). 



Uhligites kraffti (Uhlig, 1903) PI. 1, fig. 10 



1903 Streblites kraffti Uhlig: 44, pl.4, fig. 1 ; pl.5, fig. 1 . 



Material. Two specimens, CA8 15-16, from a liinestone 4 m 

 above the base of the Mintaq Member, and one, CA860, from the 

 shell bed 26 m above the base of the Arus Member, all in eastern 

 Jebel Billum. 



Description. CA815 is a well-preserved 40 mm diameter speci- 

 men; complex suture-lines, with a large lateral lobe; compressed 

 rounded venter, oval whorl section, small umbilicus, very low 

 obsolescent flexuous ribs. CAS 16 is a similar 50 mm diameter 

 specimen with complex sutures. CA860 is only 20 mm diameter. 



Remarks. U. kraffti has a narrowly rounded, not crenulated, keel 

 as in 'Gymnodiscoceras' . many of Uhlig's ( 1903) figured specimens 

 have crenulated keels, which are hollow and floored, and are missing 

 on casts of phragmocones; possibly all Uhligites have such keels, 

 and Gymnodiscoceras is a synonym. 



Occurrence and age. Arus Member and basal Mintaq Member, 

 Hajar Formation, eastern Jebel Billum: Durangites Zone, Upper 

 Tithonian. 



Family HAPLOCERATIDAE Zittel, 1884 

 Genus ft4/'Z,OC£:7MS Zittel. 1870 



Type species. Ammonites elimatus Oppel. 1868, subsequently 

 designated by Spath (1923b). 



Remarks. Dimorphism in Haploceras was described by Enay & 



