AMMONITES AND NAUTILOIDS OF WADI HAJAR 



73 



In all specimens the whorls are involute, rapidly expanding, 

 globose and massive up to 200 mm diameter, and become more 

 evolute on the final body-chamber. The whorl section is evenly 

 rounded, without a ventro-Iateral angle. Large spinose umbilical 

 tubercles give rise to broad ribs, either singly or in pairs, that are 

 prorsiradiate and fade slightly on the side of the whorl, then swell 

 in the ventro-Iateral position to fade again on the venter. A few 

 intercalated ribs commence in the middle of the whorl side. 

 Ventro-Iateral tubercles are largely absent, being limited merely to 

 the swellings in the size of the ribs at that position. The four 

 immature specimens ('?or microconchs, with last visible suture- 

 lines at the positions indicated by asterisks on PI. 11, fig. 3 and PI. 

 12, fig. 3) from Wadi Arus have depressed cadicone whorls with 

 funnel-shaped umbilici and broad rounded venters; they have only 

 6 umbilical tubercles per whorl at 23-30 mm diameter; two radial 

 ribs issue from each tubercle, a larger one that has ventro- 

 lateral swellings and passes over the venter as a rounded rib of 

 considerable size, and a smaller one that is much weaker on the 

 venter; the boldness of the larger ribs on the venter gives the whorl 

 growth a segmental appearance, ie. expanding in six segments per 

 whorl. On well-preserved parts of the shell fine growth lines can 

 be seen following the line of the ribs on both inner and outer 

 whorls. 



Measurements 



D 

 CA1046 260 



CA1046 127 



SMF. 12209 208 

 CA737 160.5 



CA741 27.5 



Wh Wb U 



92.0(0.35) — 86.0(0.33) 



61.5(0.48) 77.0(0.61) 27.5(0.22) 



86.0(0.41) 98.0(0.47) 58.0(0.28) 



73.0(0.45) 85.0(0.53) 37.3(0.23) 



13.2(0.48) 19.0(0.69) 5.9(0.21) 



CA742 



22.0 9.1(0.41) 15.3(0.70) 4.3(0.20) 



Remarks. 5. argobbae has massive globose whorls and a small 

 umbilicus that only widens on the adult body-chamber. The whorl 

 section is evenly rounded and ventro-Iateral tubercles are absent or 

 very small. These features are clear in the well-preserved example 

 of PI. 13, fig. 1, and in the larger example of PI. 14, fig. 1, where 

 the presence of the shell reveals that the umbilical tubercles are 

 spines of considerable length. Small whorls of S. argobbae have 

 not been described before, and the curious segmental growth seen 

 on those from Wadi Arus (PI. 11, fig. 3; PI. 12, fig. 3) is due to the 

 boldness of the fold-like ribs crossing the venter at these small 

 sizes. By 60 mm diameter the ribs (and their ventro-Iateral swell- 

 ings) have diminished and the line of the venter reverted to a more 

 normal smooth spiral. S. irregulare differs in being more evolute 

 in the phragmocone, having a quadrate whorl section with a flatter 

 venter, and large ventro-Iateral tubercles. A third species, S. bucki 

 Checa (1985: 175, pis 36, 37) is close to S. argobbae, but has 

 slightly less massive whorls and more ribs. It occurs in the 

 Divisum Zone at the top of the Lower Kimmeridgian in south-east 

 Spain, this being the only record of Simaspidoceras outside Ethio- 

 pia, Somalia and Yemen. 



Occurrence. Lower, middle and upper parts of the Kilya Mem- 

 ber, Naifa Formation, Wadi Arus, Naifa Cliff and Wadi Kilya; 

 Beckeri Zone, Upper Kimmeridgian, and Hybonotum Zone, Lower 

 Tithonian. 



Simaspidoceras irregulare (Dacque, 1905) PI. 13, fig. 4 



1905 Aspidoceras irregulare Dacque: 152 (not figured). 



1930 Aspidoceras irregulare Dacque; Basse; 133, pi. 4 (20), fig. 



16. 

 1943 Simaspidoceras argobbae (Dacque); Scott: 84, fig. 20; pi. 



21,fig. 2;pl. 23, fig. 1. 

 1943 Simaspidoceras harrarense Scott: 85, fig. 21; pi. 21, fig. 3; 



pi. 23, fig. 3. 

 1959 Simaspidoceras irregulare (Dacque); Venzo: 176, pi. 12, 



fig. 2. 

 1985 Simaspidoceras irregulare (Dacque); Checa: 182, figs 



II.3.46B, II.3.47C. 



Material. Three specimens from the Kilya Member; CA1049, 

 from the lower marly part in Naifa Cliff; CA1222 from the base of 

 the middle limestone part, and CA 1 22 1 from the upper marly part, in 

 Wadi Kilya. 



Description. The specimens from Wadi Kilya are large and 

 roughly preserved; one is probably incomplete at its aperture at 260 

 mm diameter; traces of a suture-line are visible half a whorl earlier 

 at 190 mm diameter, and this is probably the end of the phragmocone; 

 its inner whorls are covered in hard limestone matrix and are only 

 visible back to about \Vi whorls before the aperture; the other is a 

 short fragment of a very large body-chamber, with a whorl height of 

 103 mm, and very large umbilical and ventro-Iateral tubercles. The 

 specimen from Naifa Cliff is better preserved in dark grey limestone 

 matrix, though one side is crushed and partly absent and the earlier 

 part of the outer whorl is missing; septa are not visible on the outer 

 half whorl which is probably an incomplete body-chamber 230 mm 

 diameter at the aperture; inner whorls are exposed back to about two 

 whorls before the aperture. 



The whorls are evolute and massive; the whorl section is quadrate, 

 with nearly flat whorl sides that converge towards a broad flat venter. 

 The most prominent features of the ornament are large umbilical 

 tubercles and large bullate ventro-Iateral tubercles; broad undulating 

 ribs between the two rows of tubercles become of very low relief in 

 the middle of the whorl side. A few ribs issue in pairs from the 

 umbilical tubercles, so that there are more ventro-Iateral than um- 

 bilical tubercles. The ribs are further reduced on the outer whorls, 

 and the umbilical tubercles become more widely spaced. Measure- 

 ments of CA1049: at 170 mm: 73.5 (0.43), 84.0 (0.49), 53.5 (0.31). 



Remarks. Simaspidoceras irregulare differs from S. argobbae in 

 having more evolute whorls in the phragmocone, a quadrate whorl 

 section with a flat venter, and large ventro-Iateral tubercles. 



Occurrence. Lower, middle and upper parts of the Kilya Mem- 

 ber, Naifa Formation, Naifa Cliff and Wadi Kilya; Beckeri Zone, 

 Upper Kimmeridgian, and Hybonotum Zone. Lower Tithonian. 



Laevaptychus 



PI. 10, fig. 3; PI. 12, fig. 5; PI. 14, fig. 2 



Material. 81 specimens: 1 1 from the Mintaq Member (CA585- 

 89 from bed 29 and CA590-95 from bed 30 of the Mintaq Member 

 in the Mintaq Salt Dome); 16 from the Arus Member (CA843-58, 

 from the shell bed, 26 m above the base of that member in eastern 

 Jebel Billum); 1 from the upper marly part of the Kilya Member 

 (CA1223 from Wadi Kilya); 8 from the middle limestone part of the 



PLATE 14 



Fig. 1 Simaspidoceras argobbae (Dacque). 16.5 m above base of lower marly part of Kilya Member (fauna 7). Naifa Cliff. la-Id, CA1()46; la. lb. body- 

 chamber, xO.47; Ic, Id, wholly septate inner whorls, xO.75. 

 Fig. 2 Laevaptychus, bed 29, Mintaq Member (fauna 13), Mintaq Salt Dome. 2a, 2b, CA586. 



