98 



M.K. HOWARTH 



Suborder ANCYLOCERATINA Wiedmann, 1966 

 Superfamily ANCYLOCERATACEAE Gill, 1871 



Family ANCYLCERATIDAE Gill, 1871 

 Subfamily CRIOCERATITINAE Gill, 1871 



Genus CRIOCERATITES Leveille, 1837 



Type species. Crioceratites duvalii Leveille, 1837, subsequently 

 designated by Diener, 1925. 



Crioceratites (C.) cf. villiersianus (d'Orbigny, 1842) 



PI. 23, fig. 2 



1842 Crioceras villiersianus d'Orbigny: 462, pi. 1 14, figs 1, 2. 

 1902 Crioceras villiersianus d'Orbigny; Sarasin & 



Schondelmayer: 107, pi. 12, fig. 3. 

 1955 Crioceras villiersianus d'Orbigny; Sarkar: 65-68, pi. 3, 



figs 4, 8, pi. 5, fig. 14. 

 1964 Crioceras villiersianus d'Orbigny; Thomel: 21. 



Material. CA1298, found loose immediately below the Qishn 

 Formation in eastern Jebel Billum. The matrix indicates that it came 

 from the 5 m of sandy limestone at the bottom of the Qishn 

 Formation. 



Description. The specimen consists of nearly half a whorl from 

 an ammonite of about 90 mm diameter, and the whorl height and 

 breadth at the larger end are 34 mm and 19.5 mm respectively. It is 

 almost uncrushed, having a compressed whorl shape, flat whorl 

 sides and rounded venter, but it cannot be determined whether the 

 whorls were uncoiled or in contact. The ornament consits of fine 

 ribs, that are straight and radial on the side of the whorl, and curve 

 slightly forwards across the venter Some ribs bifurcate near the 

 umbilicus or at higher levels on the whorl side. Periodically every 

 8th to 1 2th rib is stronger or flared, especially near the umbilicus and 

 on the ventro-lateral part of the whorl side. Ventro-lateral tubecles 

 are not seen, possibly due to the poor preservation. 



Remarks. Although this ammonite was found loose just below 

 the base of the Qishn Formation in the cliff section north of the road 

 in eastern Jebel Billum, its sandy limestone matrix matches that of 

 the bottom 5 m of that formation. Its morphological features are like 

 those of the two closely similar species Crioceratites duvalii Leveille 

 and C. villiersianus d'Orbigny. Identification with the latter is made 

 on the basis of its ribs that are more numerous and finer than those 

 of the former species. C. villiersianus occurs in the upper half of the 

 Hauterivian and possibly just extends into the basal Barremian in SE 

 France according to the records of Sarkar (1955: 67) and Thomel 

 (1964: 71). C ^Mva/;/ is slightly older in the middle and upper parts 

 of the Hauterivian, and does not extend into the base of the Barremian. 

 So this is an important ammonite for establishing an Upper 

 Hauterivian age for the lower part of the Qishn Formation. 



Occurrence. Qishn Formation, lower part, eastern Jebel Billum; 

 Upper Hauterivian. 



Order NAUTILIDA Agassiz, 1847 



Superfamily NAUTILACEAE de Blainville, 1825 



Family PARACENOCERATIDAE Spath, 1927 



Genus PARACENOCERAS Spath, 1927 



Type species. Nautilus hexagonus J. de C. Sowerby, 1826. 



Paracenoceras meridionale Tintant, 1987 



PI. 23, fig. 3; PI. 24, figs 1.3 



1987 Paracenoceras meridionale Tintant: 101, fig. 21; pi. 10, 

 figs 1,2. 



Material. Five specimens: CN70-71 from the limestone con- 

 taining Erymnoceras, 17 m below the top of the Shuqra Formation 

 (ie. below the base of the Lower Storm Bed at the bottom of the 

 Madbi Formation) in central Jebel Billum; and CN68, 69 and 72 

 from the "Nautiloid Bed', 6 m below the limestone ^'MhErymnoceras 

 in the same section. 



Description. CN68 has its last septum at 185 mm diameter 

 followed by a quarter of a whorl of poorly preserved body-chamber 

 up to the aperture at about 230 mm diameter; at the final septum the 

 whorl height and breadth are 105 and 140 mm respectively. CN69 is 

 a larger isolated cast of a single air chamber between adjacent septa, 

 and the whorl height and breadth are 138 and 178 mm. CN72 is part 

 of a phragmocone up to 100 mm diameter CN70 and 71, from the 

 Erymnoceras bed, are isolated air chambers; the whorl height and 

 breadth of CN70 are 61.5 and 78.0 mm, and of CN71 are 44.5 and 

 53.5 mm respectively. All five specimens are preserved solid, CN72 

 is undistorted. but the others have been subjected to varying amounts 

 of distortion. The whorls are depressed, with whorl height/breadth 

 ratios in the range 0.75-0.85, and the umbilicus widens considerably 

 at larger sizes. The whorl section is trapezoidal, and the flat whorl 

 sides converge strongly towards a venter that has a marked sulcus, 

 which is conspicuous on whorls as small as 35 mm diameter. 



Measurements 



D Wh Wb U 



CN68 185.0 105.0(0.57) 140.0(0.76) 23.5(0.13) 



CN68 93.0 49.5(0.53) 61.5(0.66) 13.2(0.14) 



CN72 86.0 43.0(0.50) 50.0(0.58) 19.5(0.23) 



Remarks. P. meridionale is a large, depressed, ventrally sulcate 

 species, originally described from the Middle Callovian of Jebel 

 Tuwaiq, Saudi Arabia, from two septate specimens up to 138 mm 

 diameter The Yemen specimens are larger, and phragmocones that 

 are preserved up to at least 250 mm diameter indicate final diameters 

 of 375^00 mm for complete specimens. The smaller whorls show 

 that the ventral sulcus is present throughout growth. 



Occurrence. Upper part of the Shuqra Formation, central Jebel 

 Billum; Coronatum Zone, Middle Callovian (?or Upper Callovian). 



Paracenoceras cf. calloviense (Oppel, 1857) PL 24, fig. 2 



1857 Nautilus calloviense Oppel: 547. 



1873 Nautilus calloviense Oppel; Waagen: 18, pi. 3, fig. 2. 



1927 Paracenoceras cf. ca//ov/e;7ie (Oppel); Spath: 31,pl. 2, fig. 



l,pl. 3, fig. 5. 

 1969 Paracenoceras calloviense {0^pe\).TmldinV. 169-181, pis 



9-12. 

 1994 Paracenoceras calloviense (Oppel); Bardhan et at 293, 



figs 3, 4, 7, 8A-C (see for more complete synonymy). 



Material. One specimen, CN73, from the upper part of the 

 Shuqra Formafion, 1 km east of the Al Ma'abir road/river crossing. 



Description. This is a wholly septate half whorl, 75 mm diameter, 

 preserved only on one side but part of the venter is present at each 

 end. At 75 mm diameter, the whorl height is 44.5 mm, the umbilical 

 width is approximately 6 mm, but the whorl breadth is not seen due 

 to the poor preservation. The whorl sides are flat and converge 

 strongly to a flat or slightly arched venter. The suture-line has a wide, 

 shallow lateral lobe between smaller saddles at the ventro-lateral 

 and umbilical margins. 



Remarks. This specimen differs from the depressed, ventrally 

 sulcate species P. meridionale at the same horizon in the Shuqra 

 Formation in being more compressed and having a flat or slightly 



