74 



M.K. HOWARTH 



Kilya Member (CA 1050-51, SM F. 12 173, F. 12206, R 12208 and 

 F13419, from Naifa Cliff, and CA1228-29 from Wadi Kilya); 44 

 from the lower marly part of the Kilya Member (CA 1224-27 and 

 CA 1230-59 from Wadi Kilya, SM F 13420-21 from Jebel Billum, 

 CA745-46, SMR 12 159, F 13422 and R 13435 from Wadi Arus, and 

 SM R 12 174-76 from Husn Ba Qirwan); CA839 from the Lower 

 Storm Bed, Madbi Formation, central Jebel Billum. 



Remarks. These are typical thick-shelled, broad Laevaptychus, 

 punctate on the outer convex surface, and with concentric ribs on the 

 inner surface. Many are in the size range 40-60 mm long, a few are 

 70-90 mm long (PI. 14, fig. 2), and the largest is a fragment from an 

 aptychus about 120 mm long. There are several associated pairs of 

 aptychi (PI. 12, fig. 5). As aptychi mainly from Aspidoceratinae, 

 they confirm the widespread occurrence of that subfamily in the 

 Kimmeridgian, Tithonian and Berriasian of Wadi Hajar. The com- 

 monest occurrence is in the lower part of the Kilya Member in Wadi 

 Kilya, where Orthaspidoceras avellanum (Zittel) is also common. 

 There are also several large, well-preserved, Laevaptychiis in the 

 middle beds of the Mintaq Member at Mintaq of mid-Berriasian age, 

 where Aspidoceras is poorly preserved, though some are large. The 

 single specimen from the Lower Storm Bed of the Madbi Formation 

 in central Jebel Billum is of lower to mid-Oxfordian age, and is of 

 interest in showing the presence of Aspidocerafinae at that horizon, 

 probably Euaspidoceras. 



Subfamily HYBONOTICERATINAE Callomon, 1981 

 Genus HYBONOTICERAS Breistroffer, 1947 



Type SPECIES. Ammonites hybonotum Oppel, 1863. 



Hybonoticeras ornatum (Spath, 1931) 



PI. 15, fig. 1 



1930 Waagenia sp. nov., Spath; 62, text-figs 4a, 4b. 



1931 Waagenia omata Spath; 649, pi. 118, fig. 5; pi. 120, fig. 1 

 (holotype). 



1931 Waagenia africana Spath; 650 (nom. nov. for Spath, 1930; 



62. text-figs 4a, 4b). 

 71959 Hybonoticeras beckeri extraspinatum Berckhemer & 



Holder; 29, 30, figs 14, 15; pi. 4, fig. 17. 

 1984 Hybonoticeras cf. ornatum (Spath); Verma & Westermann; 



73, pi. 19, figs 3, 4. 



Material. Two specimens, CAl 260-61, from the upper marly 

 part of the Kilya Member in Wadi Kilya. 



Description. The larger specimen (CAl 260) is a fragment one- 

 third of a whorl long; septa can be seen up to 45° before the aperture, 

 and it might possibly be wholly septate up to its aperture, which is at 

 about 100 mm diameter. The second specimen is a much shorter 

 fragment of a slightly larger whorl, with a whorl height of about 35 

 mm. The robust whorls have a quadrate whorl section, with sloping 

 umbilical walls. Markedly rursiradiate ribs loop between strong 

 umbilical and ventro-lateral tubercles, and there are a few interme- 

 diate non-tuberculate ribs; from the ventro-lateral tubercles, single. 



twinned or intercalated secondary ribs project strongly forwards on 

 the venter and join coarse raised serrations that border a deep mid- 

 ventral groove. 



Remarks. Spath's holotype is from the Hybonotum Zone at Cutch, 

 and the larger holotype of Waagenia africana Spath is from Mom- 

 basa; both differ from H. beckeri (Neumayr) only in their stronger 

 ornament and broader, more robust whorls. The specimens figured 

 by Verma & Westermann ( 1 984) are two very similar fragments from 

 the bottom of the Hybonotum Zone at Mombasa. Several examples 

 of Hybnoticeras from Madagascar were figured by Collignon ( 1 959); 

 most are different (many have smooth, rather than serrate, ventral 

 keels) and the one (Collignon, 1959; pi. 106, fig. 392) which was 

 compared with H. ornatum by Verma & Westermann (1984; 75) is 

 too badly figured to be interpreted. This is the most coarsely ribbed 

 species of Hybonoticeras, and probably comes from the the lower 

 part of the Hybonotum Zone. H. beckeri is less strongly ribbed, and 

 several other species of Hybonoticeras are much less strongly 

 ribbed, striate or even smooth. 



Occurrence. Upper part of the Kilya Member, Naifa Formation, 

 Wadi Kilya; Hybonotum Zone. Lower Tithonian. 



Hybonoticeras cf. hybonotum (Oppel, 1863) PL 15, fig. 4 



1863 

 1959 



1984 



Ammonites hybnotus Oppel; 254, pi. 71, figs 1-3. 



Hybonoticeras hybonotum (Oppel); Berckhemer & Holder; 



30, fig. 16; pi.' 3, fig. 12; pi. 5, figs 18, 19 (see for 



synonymy). 



Hybonoticeras cf. hybonotum (Oppel); Verma & 



Westermann; 73, pi. 18, fig. 2. 



Material. C A 1 262 from the upper marly part of the Kilya Mem- 

 ber in Wadi Kilya. 



Description. This is a large septate fragment a quarter of a whorl 

 long, with a maximum whorl height and breadth of 45 mm and 36 

 mm respectively. It is part of a quickly expanding, massive whorl at 

 about 115 mm diameter. The whorl section is quadrate, with flat 

 sides and venter. Large umbilical tubercles and large widely spaced 

 ventro-lateral tubercles are joined by ribs, some of which are looped 

 between them, and there are many intermediate non-tuberculate 

 ribs. Weak or striate secondary ribs are projected strongly forwards 

 on the sides of the venter, and a deep ventral groove is bordered by 

 slightly raised ridges that are only weakly crenulate. 



Remarks. This large fragment is like Hybonoticeras hybonotum, 

 but the whorls are broader and expand more quickly, giving a very 

 massive appearance. The near-flat venter with a prominent groove 

 bordered by low poorly crenulate ridges is very similar to the 

 fragment from the Beckeri Zone at Mombasa figured by Verma & 

 Westermann ( 1 984; pi. 1 8, fig. 2), and they recorded other fragments 

 from the Hybonotum Zone (Verma & Westermann, 1984; 16, table 

 2). 



Occurrence. Upper part of the Kilya Member, Naifa Formation, 

 Wadi Kilya; Hybonotum Zone, Lower Tithonian. 



PLATE 15 



Fig. 1 Hybonoticeras ornatum (Spath). upper marly part of Kilya Member (fauna 8), Wadi Kilya. la, lb, CAI260. 



Fig. 2 Micracanthoceras fraudator (Zittel). microbialite boulders, Arus Member (fauna 9), east cliff, Wadi Arus. 2a, 2b, CA77 1 , body-chamber. 



Figs 3, 5 Baeticoceras morrisi sp. nov., microbialite boulders, Arus Member (fauna 9), west cliff, Wadi Arus. 3a, 3b, holotype, CA765; 5a, 5b, paratype, 



CA766. 

 Fig. 4 Hybonoticeras cf hybonotum (Oppel), upper marly part of Kilya Member (fauna 8). Wadi Kilya. 4a, 4b, CA1262. wholly septate. 

 Fig. 6 Simaspidoceras argobbae (Dacque), 16.5 m above base of lower marly part of Kilya Member (fauna 7), Naifa Cliff, CA1045, xO.56. 



