AMMONITES AND NAUTILOIDS OF WAD! HAJAR 



43 



fragment of a partly crushed body-chamber with part of the ('?adult) 

 mouth-border preserved at a diameter of about 120 mm. They all 

 have a smoothly rounded elliptical whorl-section, and a wide, open 

 umbilicus. The ornament consists only of sinuous growth striae 

 which are prominent enough near the apertures to resemble obsoles- 

 cent ribbing, and the apertures follow the line of these striae. In the 

 holotype and the fragmentary paratype the apertures are probably 

 adult mouth-borders. Traces of the final suture-line can be seen on 

 CA577, and the first lateral saddle appears to be high and complex. 



Measurements 



CA576, holotype 

 CA576, holotype 

 CA576, holotype 

 CA577, paratype 



D 



135.5 



110.0 



82.0 



117.5 



Wh 

 50.1 (0.37) 

 40.4 (0.37) 

 32.8 (0.40) 

 46.8 (0.40) 



Wb 



31.3(0.28) 

 24.2 (0.29) 

 32.4 (0.28) 



U 



45.8 (0.34) 

 37.0 (0.34) 

 25.3(0.31) 

 35.5 (0.30) 



Remarks. After a considerable amount of variation in the Lower 

 Tithonian with several species recognized, Haploceras became less 

 common and less variable in the Upper Tithonian and Berriasian, the 

 main species now being H. elimatum (Oppel). With the recognition 

 of dimorphism in the genus, H. elimatum and H. carachtheis 

 (Zejszner, 1846) were taken as macroconch and microconch respec- 

 tively of a pair, for which the earlier name, H. carachtheis, was used 

 by Enay & Cecca (1986: 52). The largest specimen of H. elimatum 

 describedby Zittel (1868: 80) was 145 mm diameter, and specimens 

 of 50-70 mm diameter have an umbilicus of 1 8-23% of the diameter. 

 Compared with these the Yemeni species has a much larger umbili- 

 cus of 30-34% of the diameter at 82-135 mm diameter. The three 

 known examples are macroconchs, and similarly widely umbilicate 

 microconchs have yet to be found. 



Occurrence. Mintaq Member, Hajar Formation, Mintaq Salt 

 Dome; Occitanica Zone, Berriasian. 



Genus GLOCHICERAS Hyatt, 1900 

 Type species. Ammonites nimbatus Oppcl, 1863. 



Subgenus GLOCHICERAS Hyatt. 1900 



Glochiceras (Glochiceras) subclausum (Oppel 1863) 



PI. 3, fig. 3 



1850 Ammonites canaliculatus Miinster; d'Orbigny: 525. pi. 



199, fig. 3. 

 1863 Ammonites subclausiis Oppel: 190, pi. 52, fig. 3. 

 1887 Ammonites subclausiis Oppel; Quenstedt: 842, pi. 92, fig. 



15. 



1901 Oppelia subclausa (Oppel): Loriol: 16, pi. 1, fig. 6 



1902 Harpoceras subclausum (Oppel); Loriol: 22, pi. 2, figs 1-3. 



1958b Glochiceras (Glochiceras) subclausum (Oppel); Ziegler: 

 107, figs 11-13; pi. 10, figs 3-5. 



Material. Five specimens, CAS 1 7-2 1 , from the lower half of the 

 Billum Member, in the road cutting at the western end of Jebel 

 Billum. 



Description. All are small tlattened specimens, the largest being a 

 complete microconch with a mouth-border and lappets at 30 mm 

 diameter, the other four being fragments of smaller specimens. The 

 whorls are involute (U/D = 0.22) and are smooth, except for a 

 prominent mid-lateral groove, which is developed at least from a 

 diameter of 12 mm and is not visible in the umbilicus on the inner 

 whorls due to the overlap of the whorls. The groove runs into the 

 slender neck of the lappet of the complete specimen, but the spatulate 

 anterior end of the lappet is not preserved. Measurements of CAS 17: 

 at 28.5 mm diameter: 13.6 (0.48), — (— ), 6.6 (0.23). 



Remarks. These ammonites were collected from loose material 

 excavated from the road cutting at the western entrance to Jebel 

 Billum. They came from lower part of the Billum Member and are of 

 interest in dating that horizon. The complete specimen is an exact 

 match for OppeFs (1863: pi. 52, fig. 3) drawing of his holotype 

 (refigured by Ziegler, 1958b: pi. 10, fig. 3), and is very like the 

 specimens figured by de Loriol (1902: pi. 2, figs 1-3). With its 

 mouth-border and lappets at 30 mm diameter it is exactly the same 

 size as the average of 1 10 microconchs from the Jura of France and 

 Germany measured by Ziegler (195Sb: 108 - average 30 mm 

 diameter, range 22-43 mm). In that area, Ziegler (1958b: 156, fig. 

 66) recorded G. (G.) subclausum from the Middle Oxfordian, 

 Transversarium Zone (White Jura lower a). From the Bimammatum 

 Zone date of the Ferisphinctids low in the Billum Member, it is 

 apparent that G. (G.) subclausum must be at least as high as 

 Bimammatum Zone inYemen. and this is an upwards extension of its 

 stratigraphical range in southern Europe. The other species of G. 

 (Glochiceras) from higher in the Upper Oxfordian and Kimmeridgian 

 described by Ziegler (1958b) lack the lateral groove on the inner 

 whorls. Hildoglochiceras is much more evolute, and its prominent 

 spiral groove is always visible on the inner whorls in the umbilicus. 



Occurrence. Lower half of the Billum Member, Naifa Forma- 

 tion, western entrance road cutting to Jebel Billum; Bimammatum 

 Zone, Upper Oxfordian. 



Subgenus LINGULATICERAS Ziegler, 1958 

 Type SPECIES. Ammonites nudatus Oppd. 1858. 



Glochiceras (Lingulaticeras) pseudocarachteis (Favre, 

 1880) PI. 1, fig. 7 



ISSO Ammonites (Haploceras) pseudocarachteis Favre: 30, pi. 

 2, fig. 11. 



PLATE 3 



Fig. 1 Haploceras umhilicatum sp. nov., bed 57, Mintaq Member (fauna 13), Mintaq Salt Dome, la, lb, holotype. CA576, xO.7. 



Fig. 2 Epimayaites sp. indet., basal 5 m of Billum Member (fauna 4). 1 km east of Al Ma'abir road/river crossing; CA1085. 



Fig. 3 Glochiceras (Glochiceras} subclausum Oppel, lower half of Billum Member (fauna 4). road cutting al western entrance to Jebel Billum. CAS 1 7. 



Figs 4, 5 Larcheria gredingensis (Wegele). 4, 7-8 m above base of Billum Member (fauna 4), Perisphinctid Cliff, eastern Jebel Billum. CA825, xO.75. 5, 



basal part of Billum Member (fauna 4), 1 km east of Al Ma'abir road/river crossing, CAI088, 

 Fig. 6 TaramelUceras (Metahaploceras) suhsidens (Fontannes), upper marly part of Kilya Member (fauna 8), Wadi Kilya. CAI()6.\ 

 Figs 7, 8 Orthosphinctes polygyratus (Reinecke), 7, 7-8 m above base of Billum Member (fauna 4). Perisphinctid Cliff, eastern Jebel Billum. CA826. 



xO.68; 8, lower half of Billum Member, road cutting at western entrance to Jebel Billum. CA836, xO.73. 

 Fig. 9 Paryphoceras grayi (Spath), basal 8 m of Billum Member (fauna 4), I km east of Al Ma"abir road crossing. CA1087. 



