46 



M.K. HOWARTH 



1961 Lithacoceras(Progeronia)pseudopoIyplocoides Gey er. 33, 



pi. 8, fig. 3. 

 1974 Perisphinctes (Orthosphinctes) polygyratus (Reinecke); 



Schairer: 51, pi. 6, figs 1-11. 

 1982 Orthosphinctes (Orthosphinctes) polygyratus (Reinecke); 



Atrops:51,pls 11-14; pi. 16, figs 1,3. 



Type. A neotype from White Jura lowery (base of Platynota Zone, 

 Lower Kimmeridgian) at Randen, northern Switzerland, was fig- 

 ured by Geyer (1961: pi. 1, fig. 4). 



Material. 4 1 specimens from the lower part of the Billum Mem- 

 ber: 20 (C.86956-60, CA 1089-1 102, SM F. 13413) from the bottom 

 5 m of the Billum Member, 1 km NE of the Al Ma'abir road/river 

 crossing; 19 (CA826-35, and 9 photographs taken in the field) 7-8 

 m above the base of the Billum Member at the Perisphinctid Cliff in 

 eastern Jebel Billum; two, CA836, 896, from west Jebel Billum, 

 near the western entrance road cutting. 



Description. All specimens are crushed and fragmentary to some 

 degree. They range up to 150 mm diameter, but three fragments that 

 have whorl heights of 80-85 mm must have been 250-275 mm 

 diameter The whorls are evolute, and the whorl section is elliptical 

 with slightly flattened sides. Strong, slightly prorsiradiate primary 

 ribs become more widely spaced on larger whorls. They divide into 

 two or three secondaries high on the side of the whorl, then pass over 

 the venter projected gently forwards but with no interruption. The 

 ratio secondary/primary ribs is 2.4-2.7/1. Occasional constrictions 

 follow the line of the ribs. 



Remarks. Schairer (1974: 51-56) had a much more extensive 

 synoymy for Orthosphinctes polygyratus, into which he placed 

 many other species as synonyms. His interpretation of the species 

 was wider than that of Geyer (1961: 21), as can be seen in the range 

 ofmorphology inthe 11 specimens that he figured (Shairer, 1974:pl. 

 6, figs 1-11). This is not the place to discuss the detailed synonymy 

 of the species, though it is worth noting that Schairer was probably 

 correct in including the type species of Orthosphinctes {Ammonites 

 tiziani Oppel, 1863) as a synonym, because comparison of the two 

 type specimens (Geyer, 1961: pi. 1, fig. 4 is the neotype of Ammo- 

 nites polygyratus; Wegele, 1929: pi. 1, fig. 4, is the lectotype of 

 Ammonites tiziani) shows them to be almost identical in all respects. 

 Good specimens of O. polygyratus cannot be obtained from the 

 lower part of the Billum Member - at all localities they are flattened 

 and often seen only as external moulds on large slabs of hard 

 limestone. Photographs taken in the field are the only record of some 

 specimens, but they show the evolute whorls and primary ribs 

 becoming more widely spaced at larger sizes, by which they differ 

 from the more involute, more densely ribbed examples of LMrcheria 

 at the same horizon. 



Occurrence. Lowest 8 m of the Billum Member, Naifa Forma- 

 tion, Jebel Billum and Al Ma'abir; Bimammatum Zone, Upper 

 Oxfordian. 



Genus TORQUATISPHINCTES Spath, 1923a, 

 p. 302 [1924a, p. 15] 



Type species. Ammonites torquatus J. de C. Sowerby, 1840. 



Remarks. Due to its small size and indifferent preservation, 

 interpretation of the holotype of the type species (re figured by Spath, 

 1 93 1 : pi. 76, fig. 4) is difficult. It could be an incomplete microconch 

 or the inner whorls of a macroconch. It does, however, have some 

 distinctive features: each of the prorsiradiate constrictions is fol- 



lowed by a simple, undivided rib, where growth increases 

 segmentally. It is possible to relate this holotype to much larger 

 ammonites, such as the undoubted microconch (possibly complete 

 at 210 mm diameter) figured by Spath (1931: pi. 76, fig. 1) as the 

 holotype (BM C. 52470) of T.jurunensis. This has idenfical features 

 to the T. for^MQ/Mj' holotype. despite Spath's( 1931: 488) claims that 

 T. jurunensis has sharper ribbing and is more densely ribbed (7^ 

 jurunensis is an internal mould; T. torquatus is a cast of an external 

 mould on which the ribs are much more rounded; the rib densities 

 are the same at the same diameter). So it is possible to interpret 

 Torqiiatisphinctes as a genus with subquadrate, evolute whorls, with 

 radial or slightly prorsiradiate primary ribs, most of which bifurcate; 

 the rib before each constriction trifurcates; and each constriction is 

 followed by a single rib, where the whorl size increases segmentally. 

 It was found to be a useful genus by Krishna & Pathak (1993: 229), 

 who described species from the Divisum up to the Beckeri Zones in 

 Cutch, where they appear to be the ancestors of Pachysphinctes in 

 the Eudoxus and Beckeri Zones. 



Torquatisphinctes naifaensis sp. nov. 



PI. 2, figs 1,2 



Holotype. CA974, 13.5 m above the base of the Kilya Member, 

 Naifa Cliff. 



Paratypes. Three: CA975-76 are from the same horizon and 

 locality as the holotype; the third is SM F. 12 168, from the Breadloaf 

 Concretions in the lower part of the Kilya Member, east side of Wadi 

 Arus. 



Other material. Fragments of four specimens, CA977-80, were 

 obtained from the same horizon and locality as the holotype. 



Diagnosis. Evolute whorls, with strong, straight, radial primary 

 ribs, mostly bifurcating at the ventro-lateral edge. Growth is some- 

 what segmental at the 3^ constrictions per whorl. 



Description. The holotype is preserved solid on one side, but is 

 slightly crushed on the other; it has a final septum at 65 mm 

 diameter, then a body-chamber 280° long, and is 1 10 mm diameter 

 at its aperture, where the mouth-border is probably present on one 

 side; it is probably a near-adult microconch. The whorls are evolute 

 and serpenticone. and circular in cross-section. Most of the strong, 

 straight, radial primary ribs bifurcate at the ventro-lateral position. 

 There are a few single ribs, most immediately following the 3^ 

 constrictions per whorl, and the rib before each constriction has a 

 third secondary that branches off the primary low down on the side 

 of the whorl before the main bifurcation; the single rib following 

 each constriction is angled further forwards, and the growth of the 

 whorl increases segmentally at this point. Rib-density is fairly low- 

 51 ribs per whorl at 109 mm diameter, 44 at 66 mm, 40 at 47 mm, 39 

 at 33 mm. The paratypes from Naifa Cliff are both crushed flat; they 

 are 63 mm and 55 mm diameter, and show all the features of the 

 holotype, including the disfinctive constrictions and low rib-densi- 

 ties. The paratype from Wadi Arus is an external mould of an 

 uncrushed larger specimen, about 145 mm diameter, and shows the 

 same features including the constrictions; it has 53 ribs per whorl at 

 138 mm diameter, and 52 at 105 mm diameter; suture-lines are not 

 visible on casts made from this mould. 



Measurements 



D Wh Wb U 



CA974, holotype 104.0 30.0(0.29) 26.3(0.25) 53.0(0.51) 



CA974, holotype 64.0 17.4 (0.27) 17.2 (0.27) 33.8 (0.53) 



C.24959, T. torquatus 63.0 21.5(0.34) 22.4(0.36) 28.3(0.44) 

 holotype 



