AMMONITES AND NAUTILOIDS OF WADI HAJAR 



87 



there are many intercalated secondary ribs; in fact 6 primary ribs 

 correspond to 30 secondary ribs on this body-chamber. 



Remarks. In referring Schneid's (I9I4: pi. 4, fig. 3) finely-ribbed 

 specimen to the same species as OppeFs (1863: pi. 74, fig. 1) 

 lectotype in which the primary ribs become widely spaced at a 

 smaller size, a considerable amount of variation is admitted toL (L.) 

 ulmense. The larger Yemeni specimen (SM F. 12202) has widely 

 spaced primaries and 5 times as many secondary ribs, just as on the 

 last quarter-whorl of the lectotype at a similar size. CA1264 from a 

 higher horizon at Al Ma'abir has fine ribs persisting to about 140 mm 

 diameter, and greatly resembles Schneid's specimen. The presence 

 of this well-dated species at Naifa Cliff and Al Ma'abir is confirma- 

 tion of the zonal age indicated by the accompanying ammonites. 



Occurrence. Middle and upper parts of the Kilya Member, Naifa 

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

 Kimmeridgian and Hybonotum Zone, Lower Tithonian. 



Subgenus SUBPLANITES Spath, 1925 



Type species. Virgatosphinctes (Perisphinctes) reisi Schneid, 

 1915. 



Remarks. The type specimen of the type species of Subpkmites 

 (Schneid, 1915: pi. 8, fig. 2) is an incomplete microconch, 165 mm 

 diameter. Some authors (Zeiss, 1968: 162-63; Ohmert & Zeiss, 

 1980: 12) believe that such microconchs commonly accompany the 

 much larger macroconchs of Lithacoceras s.s., and Subplanites has 

 been given subgeneric status by those who use different names for 

 macroconchs and microconchs in Upper Jurassic ammonites. 



Lithacoceras (Subplanites) mombassanum (Dacque, 

 1910) PI. 19, figs 1,2; PI. 20, fig. 7 



1910 Lithacoceras {Subplanites) mombassamun Dacque: 15, 



pi. 3, fig. 4; pi. 4, fig. 1. 

 1925 Perisphinctes cf. abadiensis Choffat; Stefanini: 148, pi. 



27, fig. 3. 

 1930 Lithacoceras mombassanum (Dacque); Spath: 48, pi. 4, 



fig. 1. 

 1930 Lithacoceras torquatiforme Spath: 49, pi. 4, fig. 14. 

 1930 Lithacoceras mackinnonwoodi Spath: 49, text-fig. 2. 

 1930 Lithacoceras roubvanum (Fontannes); Spath: 5 1 , text-fig. 



3. 

 1943 Lithacoceras mombassanum (Dacque); Scott: 71, pi. 14, 



fig. 1. 

 ? 1959 Lithacoceras mombassanum (Dacque), var. antrobikense 



Collignon: pi. 90, fig. 359. 

 no/7 1959 Lithacoceras mombassanum (Y)7icq\i€)\Vtnzo: 124, pi. 2. 



figs 4, 5: pi. 3, fig. 1. 

 1984 Lithacoceras? mombassanum (Dacque);Verma &Wester- 



mann: 49, pi. 8, fig. 1. 



Type. Spath ( 1 930: 48) designated the original of Dacque. 1910, 

 pi. 4, fig. 1, as lectotype. 



Material. 38 specimens from the Kilya Member: CA 1 270 from 

 the upper mariy part in Wadi Kilya: CA 1265-69 from the middle 

 limestone part in Wadi Kilya; SM F 12 198, F 12207, F 134 14 and 

 F 1 6 1 1 from the base of the middle limestone part in Naifa Cliff; 26 

 (including CA1271-85) from the lower mariy part in Wadi Kilya, 

 and SM F. 12165-66 from the Breadloaf Concrefions in the east cliff 

 of Wadi Arus. 



Description. All are fragments or incomplete specimens up to 

 200 mm diameter. Parts of body-chambers are preserved in some of 

 the uncrushed specimens, but none have any adult features. The 26 

 specimens from the lower marly part of the Kilya Member in Wadi 

 Kilya are laterally crushed fragments from a shell bed and are from 

 whorls of up to 100 mm diameter. The whoris are slightly involute, 

 and the whorl section is oval and higher than broad. The primary ribs 

 are radial or slightly prorsiradiate, and are straight, but tend to 

 become curved at larger sizes. On whorls of up to 1 00 mm diameter 

 most of the primary ribs bifurcate high on the whorl side, and the 

 secondaries pass radially over the evenly arched venter without 

 interruption; a very few ribs remain single. At sizes larger than 100 

 mm diameter, a few ribs trifurcate, or an extra secondary rib is 

 intercalated. Numbers of primary/secondary ribs in six specimens 

 are: 29 primaries/60 secondaries at 185 mm diameter, 35/77 at 130 

 mm, 12/30 at 160 mm, 14/28 at 128 mm, 20/41 at 100 mm, 15/28 at 

 90 mm (these are not ribs per whorl; they are counts along dift'erent 

 lengths of whori mostly less than half a whori long, and the diam- 

 eters are the approximate sizes at the larger end); the average ratio 

 primaries/secondaries is 1/2.1. 



Measurements 



D 

 SMF12198 190.0 

 CA1265 134.5 



Lectotype 101.0 



Wh Wb U 



56.0(0.29) 48.2(0.25) 90.0(0.47) 



41.2 (0.31) 34.3 (0.25) 62.0 (0.46) 



31.0(0.31) — 45.0(0.45) 



Remarks. These ammonites are more involute, have more com- 

 pressed, more rounded whorls, and more primary ribs which 

 occasionally trifurcate, than those species of Pachysphinctes that 

 occur at the same horizon. Although none show any adult features, 

 even the biggest of them could be a microconch, which attain very 

 large sizes in some species, eg. the 190 mm diameter microconch 

 with lappets of Lithacoceras (Subplanites) postrueppelianum Ohmert 

 & Zeiss (1980: 29, pi. 13, fig. 2). The latter species is from the 

 Hybonotum Zone in south-west Germany, and although closely 

 similar to L. (S.) mombassanum, it is more involute, has straighter 

 primaries and many more secondary ribs than the latter species. L. 

 (S.) mombassanum is common in the Eudoxus and Beckeri Zones 

 (in the Changamwe Shales) at Mombasa, and it may extend into the 

 Hybonotum Zone (Verma & Westermann, 1984: 49). Another genu- 

 ine example of the species appears to be the specimen from Ethiopia 



PLATE 19 



Figs 1, 2 Lithacoceras (Subplanites) mombassamun (Dacque), base of middle limestone part of Kilya Member (fauna 7). Naifa Cliff, la, lb, SM 

 F. 161 10a. 2a, 2b, SM F 12198. body-chamber, xO.66. 



Figs 3, 4 Berriasella (Berriasella) oppeli (Kilian), shell bed 26 m above base of Arus Member (fauna 10), eastern Jebel Billum. 3, CA915. 4, CA914. 



Fig. 5 Substeueroceras koeneni (Steuer), shell bed 26 m above base of Arus Member (fauna 10). eastern Jebel Billum. 5a, 5b, CA940. 



Fig. 6 Lithacoceras (Lithacoceras) cf. ulmense (Oppel), base of middle limestone part of Kilya Member (fauna 7). Naifa Cliff 6a, 6b, SM F. 12202, body- 

 chamber, xO.67. 



Figs 7, 9 Berriasella (Berriasella) cf. oxyrosta Mazenot, microbialite boulders. Arus Member (fauna 9), Wadi Arus. 7, east cliff, CA776. 9a, 9b, west 

 cliff. CA777. 



Fig. 8 Berriasella (Berriasella) aff. chomeracensis (Toucas). bed 60, Mintaq Member (fauna L^). Mintaq Salt Dome. 8a, 8b, CA67.'^. body-chamber with 

 lappets. 



