. Bulletin of the Natural Histort Museum. Geology series. AMMONITES AND NAUTILOIDS OF WADI HAJAR 39. Fig. 1 Steblites plicodisciis (Waagen). on limestone pavement formed by top bed of Billum Member (fauna 6). below west cliff. Wadi Arus; (from a colour photograph taken in the field). some. The whorls arc involute oxycones, with an angled or bluntly rounded venter. At sizes of 50-100 mm diameter the whorl height is 52-56% of the diameter and the umbilical width is 11%. Feeble falcoid ribs or striae can be seen crossing parts of the side of the whorl, though they are very weak in the middle
. Bulletin of the Natural Histort Museum. Geology series. AMMONITES AND NAUTILOIDS OF WADI HAJAR 39. Fig. 1 Steblites plicodisciis (Waagen). on limestone pavement formed by top bed of Billum Member (fauna 6). below west cliff. Wadi Arus; (from a colour photograph taken in the field). some. The whorls arc involute oxycones, with an angled or bluntly rounded venter. At sizes of 50-100 mm diameter the whorl height is 52-56% of the diameter and the umbilical width is 11%. Feeble falcoid ribs or striae can be seen crossing parts of the side of the whorl, though they are very weak in the middle part of the whorl side and more prominent near the venter. Remarks. Waagen's sole original specimen was only 31 mm diameter, but Spath re-interpreted the species from more than 20 larger well-preserved specimens, which he claimed showed the complete range from small 'smooth young to smooth adult" (Spath, 1928: 148), some of which were still septate at 110 mm diameter. The ribs are always feeble except for the forwardly inclined cres- cents at the ventral edge. The amount of variation in rib strength is not clear from either the original Cutch or the present Yemen specimens, so it is not clear whether Strehlites habyensis Spath (1928: 151, pi. 8 fig. 1) with its slightly stronger ribs is a synonym, though the nearly smooth species S. leptodiscus Spath (1928: 150, pi. 16, fig. 1) does not appear to be different. Their age in Cutch is Eudoxus and Beckeri Zones. Specimens that almost certainly be- long to the same species were described by Verma & Westermann (1984) from the Hybonotum Zone at Mombasa, and several speci- mens from the same Eudoxus to Hybonotum Zone age range were described by Collignon (1959) from Madagascar. Occurrence. Top bed of the Billum Member, Naifa Formation, west cliff of Wadi Arus; Eudoxus or Beckeri Zones, Upper Kimmeridgian. aptychi of the family Oppeliidae. they are probably from Tara- melliceras, species of which occur in both parts of the Kil
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Keywords: ., bhlconsortium, bookc, bookcentury1900, bookcollectionbiodiversity
