AMMONITES AND NAUTILOIDS OF WADI HAJAR 



79 



Family HIMALAYITIDAE Spath, 1925 

 Genus AULACOSPHINCTES Vhlig, 1910 



Type species. Ammonites moerikeanus Oppel, 1 863, subsequently 

 designated by Spath, 1924a. 



Aulacosphinctes spitiensis (Uhlig. 1910) 



PI. 13. fig. 3 



1910 Perisphinctes {Aulacosphinctes} spitiensis Uhlig: 351. pi. 



33, figs 1,3; pi. 41, fig. 1. 

 1960 Aulacosphinctes cf. spitiensis Uhlig var. mitlticostata 



Collignon: pi. 170, fig. 712. 



Material. CA768 from the microbialite boulders, Arus Member, 

 east side of Wadi Arus. 



Description. A small specimen, 51 mm diameter, with parts of 

 the umbilical wall preserved up to about 60 mm diameter. The last 

 suture is 0.75 whorls before the present aperture, so it may have 

 had about one whorl of body-chamber when complete. The whorls 

 are evolute and have a subquadrate whorl-section. The primary 

 ribs are sharp and well spaced, and most of them bifurcate on the 

 outer half of the whorl side; there are about 15 primary ribs per 

 half whorl at 43 mm diameter. The secondaries are angled for- 

 wards over the arched venter, and there is a well-formed groove in 

 the centre of the venter. 



Remarks. This single ammonite is closely similar to the smallest 

 and best-preserved of Uhlig's (1910: pi. 33, fig. 1) original speci- 

 mens, which were from the Upper Tithonian of Spiti. The ammonite 

 from the Upper Tithonian of Madagascar that Collignon (1960: fig. 

 712) figured as var. multicostata also appears to be the same, while 

 the specimen that he (Collignon, 1960: fig. 718) determined as 

 Aulacosphinctes cf. spitiensis is more involute and his finer primary 

 ribs. 



Occurrence. Microbialite boulders, Arus Member, Hajar For- 

 mation, Wadi Arus; Microcanthum Zone, Upper Tithonian. 



Aulacosphinctes natricoides (Uhlig, 1910) PI. 13, fig. 2 



1910 Perisphinctes (Aulacosphinctes) natricoides Uhlig: 355, pi. 

 32, fig.3;pl. 41,fig. 2. 



Material. Two specimens, CA769-70, from the microbialite 

 boulders, Arus Member, west side of Wadi Arus. 



Description. CA769 is 47 mm diameter, CA770 is a short frag- 

 ment of a whorl of similar size, and the presence or absence of septa 

 cannot be determined in either. The whorls are evolute and have a 

 subquadrate whorl-section. Most of the sharp primary ribs bifurcate 

 near the ventro-lateral angle, though a few remain single; there are 

 about 21 primary ribs per half whorl at 43 mm diameter. The 

 secondary ribs weaken in the centre of the venter, but they are not 

 clearly interrupted. 



Remarks. Aulacosphinctes natricoides differs from A. spitiensis 

 in having denser primary ribs, and secondary ribs that are more 

 continuous across the venter with only a slight mid-ventral depres- 

 sion. In fact/4. natricoides is one of the few species oi Aulacosphinctes 

 that has a poorly developed mid-ventral depression. The ammonite 

 from the Tithonian of Madagascar figured by Collignon (1960: pi. 

 1 7 1 , fig. 7 1 9) asA. natricoides warobliqua appears to be too coarsely 

 ribbed to belong to this species. 



Occurrence. Microbialite boulders, Arus Member, Hajar For- 

 mation, Wadi Arus; Microcanthum Zone, Upper Tithonian. 



Genus MICRACANTHOCERAS Spath, 1925 

 Type species. Ammonites microcunthus Oppel, 1865. 



Micracanthoceras fraudator (Zittel, 1868) PI. 15. fig. 2 



1868 Ammonites fraudator Zittel: 1 10, pi. 21. figs 2 (lectotype, 



designated Sapunov, 1979: 194), 3 (non fig. 1). 

 1890 //o/7/(7e5W(crocan//u(s(Oppel);Toucas:608,pl. 18, fig. 12. 

 1939 Himalayites (Micracanthoceras) microcanthum (Oppel); 



Mazenot: 233, pi. 37, fig. 2. 

 1979 Himalayites (Micracanthoceras) fraudator (Zittel); 



Sapunov: 194, pi. 58, fig. 5. 

 1982 Himalayites (Micracanthoceras) fraudator (Zittel); 



Nikolov: 213, pi. 77, fig. 2. 



Material. C A77 1 from the microbialite boulders near the base of 

 the Arus Member, east side of Wadi Arus. 



Description. This is a well-preserved, uncrushed fragment of a 

 body-chamber one-third of a whorl long, about 65 mm diameter, and 

 has part of the poorly preserved next inner septate whorl attached; 

 the whorl height and breadth are 16.8 mm and 16.7 mm respectively 

 at the larger end. The whorls are evolute, and the whorl section is 

 subtrapezoidal over the ventro-lateral and ventral tubercles. The 

 primary ribs are strong and slightly curved; they mostly bifurcate at 

 a prominent ventro-lateral tubercle, and the short secondary ribs all 

 end at a prominent ventral tubercle bordering a well-marked mid- 

 ventral groove. A few primary ribs remain single; on the one-third of 

 a whorl preserved, there are 2 single and 13 bifurcating ribs. 



Remarks. In M. microcanthum. the type species of Micracantho- 

 ceras, single and bifurcating primary ribs approximately alternate. 

 Micracanthoceras fraudator is closely similar and differs only in 

 having many more bifurcating than single ribs. Both species occur 

 in, and are characteristic of, the Microcanthum Zone, the lower half 

 of the Upper Tithonian. 



Occurrence. Microbiahte boulders, Arus Member, Hajar For- 

 mation, Wadi Arus; Microcanthum Zone, Upper Tithonian. 



Genus HIMALAYITES [Uhlig MS] Boehm, 1904 



Type species. Himalayites treubi Boehm, 1904, subsequently 

 designated by Douville (1912c: 262). 



Himalayites sp. indet. 



Description. C A772 is a quarter-whorl fragment of one side of a 

 whorl at 80-90 mm diameter, from the microbialite boulders in the 

 Arus Member in the western cliff in Wadi Arus. It has an evolute 

 whorl, a circular whorl section and straight primary ribs, some of 

 which remain single, while others bifurcate or trifurcate at large 

 mid- to ventro-lateral tubercles. This is the morphology of 

 Himalayites, which is characterisitic of the Upper Tithonian. 



Occurrence. Microbialite boulders, Arus Member, Wadi Arus; 

 Microcanthum Zone, Upper Tithonian. 



Family OLCOSTEPHANIDAE Pavlow, 1892 



Subfamily SPITICERATINAE Spath, 1924b 



Genus SPITICERAS Uhlig. 1903 



Subgenus SPITICERAS Uhlig, 1903 



Type species. Ammonites spitiensis Blanford, 1863 



