AMMONITES AND NAUTILOIDS OF WADI HAJAR 



83 



and 628-30 from bed 60, and CA663 from bed 69, from the Mintaq 

 Member, Mintaq Salt Dome. 



Other material. A further 55 specimens were collected: CA608- 

 10 from bed 27; CA611 from bed 29: CA612-13 from bed 30; 

 CA614 from bed 34; CA615-18 from bed 36; CA620, 622-25, 627 

 and 631-59 from bed 60 (35 specimens); CA660-62 and 664-65 

 from bed 69; CA667-69 from bed 75; and CA670 from bed 77 in the 

 Mintaq Member, Mintaq Salt Dome. 



Diagnosis. The whorls are about half involute, and have a trigonal 

 whorl section with flat converging whorl sides and a flat venter; 

 ornament consists of small to large umbilical tubercles, from which 

 prorsiradiate ribs issue; the ribs fade variably on the side of the 

 whorl; at larger sizes the outer part of the whorl and the venter are 

 smooth except for striae in some specimens. 



Description. Many specimens are fragments, and the maximum 

 measurable whorl height is 72 mm, indicating a diameter of about 

 205 mm, but a fragment of the venter of a body-chamber is from a 

 larger specimen about 250 mm diameter. The holotype is one of 

 three specimens that appear to have complete mouth borders, at 

 107.5 mm (the holotype), ca. 135 mm, and 89 mm diameter respec- 

 tively; these mouth-borders are slightly flared, but plain, so the 

 specimens are probably macroconchs. Lappets are not preserved in 

 any specimens, and parts of suture-lines are visible only rarely. The 

 whorls are moderately evolute, and the whorl section is characteris- 

 tically trigonal, with a steep umbilical wall and near-flat whorl sides 

 that converge to a fairly broad flat venter. The ornament is variable: 

 radially elongated umbilical tubercles are typically large and widely 

 spaced, but may be moderate in size or even small in some examples; 

 bold, slightly prorsiradiate, fold-like ribs issue from each tubercle 

 and most of them quickly bifurcate or trifurcate; on the outer half of 

 the whorl one to three secondary ribs may be intercalated between 

 the primary ribs; ribs cross the venter as low undulating folds or 

 striae, or both. In most specimens the ribs are progressively reduced 

 from 60-80 mm diameter, except for a few individuals that retain 

 large single fold-like ribs up to at least 125-130 mm diameter. There 

 are two or three constrictions per whorl following the line of the ribs, 

 but they are not very prominent. 



Measurements 



CA666, holotype 

 CA626, paratype 

 CA630, paratype 

 CA663, paratype 



Remarks. With 63 specimens collected, this is the commonest 

 ammonite at Mintaq. It is strangely variable in ornament, and if only 

 3 or 4 specimens had been collected in isolation, they might well 

 have been given 3 or 4 new specific names. However, the full range 

 of variation occurs at a single horizon (bed 60, from which 41 

 specimens were obtained), and many intermediates occur between 

 the different morphologies. Perhaps this is the normal range of 

 variation in a species of Spiticeras, for which extensive single 

 horizon collections have rarely, if ever, been obtained before. 

 Spiticeras pricei is similar to S. laeve Gerth (1925: 69, pi. 2, fig. 



D Wh Wb U 



95.5 34.7 (0.36) 27.7 (0.29) 35.5 (0.37) 



68.0 25.5(0.37) 22.2(0.33) 27.6(0.41) 



70.8 27.0(0.38) 23.1(0.33) 24.6(0.35) 



52.2 21.2(0.41) 17.6(0.34) 15.8(0.30) 



6), which occurs in the Berriasian of Argentina, associated with 

 Argentiniceras, but Gerth's species has fewer umbilical tubercles 

 and does not have the trigonal whorl section of S. pricei. The 

 smoothest Spiticeras in Spiti are S. suhcautleyi (Uhlig, 1903: 106, 

 pi. 12, fig. 2; pi. 13, fig. \)iindS. planus (\}\\\\g, 1903: 99, pi. 15, fig. 

 2), but both have more persistent ribbing, especially on the ventral 

 half of the whorl. The converging flat sides and tlat venter of S. 

 pricei are the same as in S. gregoryi Spath ( 1925: 152, pi. 15, fig. 9) 

 from the Tithonian of Bihendula, Somalia, but the latter has much 

 more persistent and finer ribs on the sides of the whorl and the venter. 

 None of the European Spiticeras described by Djanelidze (1922) 

 and others have the combination of the distinctive whorl section and 

 smooth whorls of 5. pricei. In the genus Groebericeras loss of 

 ornament is taken a stage further, with the whorls becoming entirely 

 smooth in later growth stages, and S. pricei might be considered to 

 be a forerunner of that morphology. 



Occurrence. Mintaq Member, Hajar Formation, Mintaq Salt 

 Dome; Occitanica Zone, Berriasian. 



Spiticeras (Spiticeras) gregoryi (Spath, 1925) PI. 17, fig. 5 



1925 Bihenduloceras gregoryi Spath: 152, pi. 15, fig. 9. 



Material. CA773 from the microbialite boulders in the Arus 

 Member on the west side of Wadi Arus. 



Description. This is fragment of a whorl at 20-25 mm whorl 

 height and about 70 mm diameter, and part of an inner whorl is 

 attached. It has a quadrilateral whorl section, in which whorl sides 

 converge slightly to a broad, flat venter. Prorsiradiate ribs issue in 

 bundles of 4— 6 from large umbilical tubercles; they are continuous 

 across venter with some weakening and a slight backwards bend at 

 the centre. Septa or suture-lines are not preserved. 



Remarks. The features that can be seen on this fragment are 

 identical with those of Spath's unique holotype, except for the very 

 slight backwards bend in the ribs in the middle of the venter. Spath's 

 specimen came from Bihendula, Somalia, not associated with other 

 ammonites and he determined the age as 'Tithonian?" from its 

 morphology. 



Occurrence. Microbialite boulders, Arus Member, Hajar For- 

 mation, west side of Wadi Arus; Microcanthum Zone, Upper 

 Tithonian. 



Spiticeras (Spiticeras) sp. indet. 



Material. Five specimens: CA601-02 from bed 36, CA603 from 

 bed 57 and CA671 from bed 60 of the Mintaq Member, Mintaq Salt 

 Dome; CA859 from a shell bed 26 m above the bottom of the Arus 

 Member, eastern Jebel Billum. 



Remarks. Although these Spiticeras are not well enough pre- 

 served to be identified specifically, the one from the Arus Member in 

 Jebel Billum is important in providing age information for that level, 

 and the others appear to show the presence of species not otherwise 

 represented in the collections. Thus the two large specimens (CA601- 

 02) from bed 36 in the Mintaq Salt Dome clearly belong to two 



PLATE 18 



Figs 1, 2 Spiticeras pricei sp. nov., Mintaq Member (fauna 1 3). Mintaq Salt Dome, la, lb, holotype, CA666 from bed 75. body-chamber. 2a, 2b, CA661 



from bed 69, body-chamber. x0.80. 

 Fig. 3 Spiticeras (Negreliceras) obliquenodosum (Retowski), bed 36, Mintaq Member (fauna 13), Mintaq Salt Dome, CA604. 

 Fig. 4 Virgatosphinctes cf. broilii (Uhlig). shell bed, 26 m above base of Arus Member (fauna 10), eastern lebel Billum. CA862. 

 Fig. 5 Choicensisphinctes limitis (Burckhardt). 4 m above base of Mintaq Member (fauna 1 1 ), eastern Jebel Billum, CA908, xO.68. 



