88 



M.K. HOWARTH 



figured by Scott (1943: pi. 14, figs 1, 2), but L. mombassanum, var. 

 antrobikense Collignon (1959: pi. 90, fig. 359) from Madagascar is 

 more doubtful because of the number of single ribs (30 primaries, 54 

 secondaries per half whorl at about 80 mm diameter) and its alleged 

 Upper Oxfordian age. 



Occurrence. Lower, middle and upper parts of the Kilya Mem- 

 ber, Naifa Formation, Wadi Kilya, Naifa Cliff and Wadi Arus; 

 Beckeri Zone, Upper Kimmeridgian, and Hybonotum Zone, Lower 

 Tithonian. 



Subfamily VIRGATOSPHINCTINAE Spath, 1923a 

 Genus VIRGATOSPHINCTES Uhlig, 1910 



Type species. Perisphinctes { Virgatosphinctes) broilii Uhlig, 1910, 

 subsequently designated by Douville, 1912a, p. 737. 



Virgatosphinctes cf. broilii (Uhlig, 1910) 



PI. 18, fig. 4 



1910 Perisphinctes (Virgatosphinctes) broilii Uhlig: 336, pi. 91, 



fig. 1. 

 1971 Virgatosphinctes cf. broilii (Uhlig); Mouterde: 157, pi. 3, 



fig. 2. 



Material. 36 specimens: 22 fragments, CA861-82, mainly 

 crushed, from the shell bed. 26 m above base of the Arus Member, 

 and 13 specimens, CA883-95, from a bed of limestone 4 m above 

 the base of the Mintaq Member, both at eastern Jebel Billum; CA775 

 from the microbialite boulders in the Arus Member in the east cliff 

 of Wadi Arus. 



Remarks. It is not possible to identify this crushed or fragmentary 

 material accurately. They do, however, have the round whorl section 

 and the fine, sharp ribs of Virgatosphinctes, which either bifurcate 

 once or twice in virgatotome fashion. In general, the degree of 

 involution of the whorls and the rib density agrees closely with 

 Uhlig's (1910: pi. 91. fig. 1) figure of the holotype of the type 

 species, V. broilii, and the secondary ribs appear to pass over the 

 venter with only a slight weakening along the central line. 



Occurrence. Arus and basal Mintaq Members, Hajar Forma- 

 fion, eastern Jebel Billum and Wadi Arus; Microcanthum and 

 Durangites Zones, Upper Tithonian. 



Genus CHOICENSISPHINCTES Leanza, 1980 

 Type species. Perisphinctes choicensis Burckhardt, 1903. 



Choicensisphinctes limitis (Burckhardt, 1930) 



PI. I8,fig. 5;P1. 20, fig. 9 



1900 Perisphinctes aff. erinus (d'Orbigny); Burckhardt: 42, pi. 

 26, fig. 3 (photograph of the holotype); pi. 29, fig. 13 {nan 

 pi. 25, fig. 1, pi. 29, fig. 12 = holotype of Perisphinctes 

 erinoides Burckhardt, 1903). 



1903 Perisphinctes aff. erinus (d'Orbigny); Burckhardt: 52, pi. 8, 



fig. 5; pi. 9, figs 1, 2 (drawing of the holotype). 

 1930 Craspedites limitis Burckhardt: 110 [nom. nov. for 



Perisphinctes aff. erinus (d'Orbigny); Burckhardt, 1900: 



42). 

 1 980 'Perisphinctes ' aff. erinus (d'Orbigny ) Burckhardt; Leanza: 



35. 

 1981b Choicensisphinctes erinus (Burckhardt, non d'Orbigny); 



Leanza: 571. 



Material. 17 specimens: 8, CA897-904, from the shell bed 26 m 

 above the base of the Arus Formation, and 9, CA905-13, from the 

 limestone 4 m above the base of the Mintaq Member, both in eastern 

 Jebel Billum. 



Description. CA905 is an uncrushed quarter-whorl fragment of a 

 phragmocone at about 1 30 mm maximum diameter, with parts of the 

 inner whorls attached. All the others are less well preserved and 

 often crushed, and most are fragments from a shell bed; two of them 

 are remains of specimens about 200 mm diameter. The whorls are 

 moderately involute and inflated, and have a trapezoidal whorl 

 section in which the rounded whorl sides converge to a rounded 

 venter; the greatest whorl breadth is near the umbilical edge. Sharp 

 ribs on the inner whorls divide into two to six secondary ribs on the 

 outer part of the whorl; occasional ribs are twinned from the 

 umbilical edge. From about 100 mm diameter the primary ribs 

 become widely spaced bulges on the umbilical half of the whorl that 

 are vaguely connected with the many more indistinct secondary ribs 

 that cross the venter; the ribs fade further at larger sizes leaving only 

 bulges on the dorsal half of the whorl. 



Remarks. Choicensisphinctes is the generic name given to three 

 closely related species (C. choicensis (Burckhardt, 1903), C. 

 erinoides (Burckhardt, 1903), and C. limitis (Burckhardt, 1930)) 

 that are more involute and more inflated than Virgatosphinctes, and 

 tend to become smooth at large sizes, except for large umbilical 

 bulges. Choicensisphinctes limitis has the most involute and massive 

 whorls of the three species; it also has a trapezoidal whorl section 

 and loses its ribs more quickly than the others. A feature of 

 Choicensisphinctes is that occasional ribs (?one or two per whorl) 

 are twinned from the umbilical edge, as can be seen on several of the 

 specimens figured by Leanza (1980: pi. 3, fig. 1 ; pi. 4, figs 1 , ?3), and 

 also on three of the Yemen specimens (including PI. 20, fig. 9). 



Choicensisphinctes occurs in western Argentina, and apart from a 

 possible record (unfigured) of C. cf. choicensis in central Turkey 

 (Enay et al, 1 97 1 : 408) this is the first record from outsideArgentina. 

 Choicensisphinctes is from the Mendozanus Zone according to 

 Leanza (1980: 13ff; 1981b: 571), which is the lowest part of the 

 Tithonian following the Tithonian transgression in Neuquen and 

 Mendoza. According to Zeiss (1968: 136) this is correlated with the 

 Parapallasiceras palatinum Zone in Franconia, which is the top of 

 his Lower Tithonian, below his Middle Tithonian Semiforme 

 (=Bavaricum) Zone. [In the correlation table of Howarth, 1992: 600, 

 table 2, the South American Mendozanus Zone should be correlated 

 with only the top half of the Darwini Zone, because there is no older 



PLATE 20 



Figs 1, 2 Berhasella (Elenaella) sevenieri (Le Hegarat). Mintaq Member (fauna 13), Mintaq Salt Dome, la, lb, CA674 from bed 36. 2a, 2b, CA675 



from bed 60, '?wholly septate. 

 Figs 3, 5, 6 Substeuemceras striatum sp. nov. 3, top of bed 1. 25 m above base of Mintaq Member (fauna ?I2), Mintaq Salt Dome, CA684. 5, 6, 



paratypes. 55 m above base of Mintaq Member (fauna 12), road gorge at southern end of Wadi Arus; 5. CA787, body-chamber with lappet; 6, CA791. 

 Figs 4, 8 Mulhosiceras cf. aizyensis Mazenot, shell bed 26 m above base of Arus Member (fauna 10), eastern Jebel Billum. 4, CA932; 8, CA933. 

 Fig. 7 Lithacoceras (Subplanites) momhassaiwm (Dacque), Breadloaf Concretions. Kilya Member (fauna 7), east cliff, Wadi Arus. 7a, 7b, SM F.12166. 

 Fig. 9 Choicensisphinctes limitis (Burckhardt), 4 m above base of Mintaq Member (fauna 1 1 ), eastern Jebel Billum, CA905, wholly septate. 



