60 



M.K. HOWARTH 



Fig. 3 Idoceras cf. hanirinum Venzo. whorl cross-sections of CA1034 of 

 PI. 9, fig. 1 ; A, at 128 mm whorl height and about 430 mm diameter; B, 

 at 1 14 mm whorl height and 320 mm diameter; C, at 100 mm whorl 

 height and 270 mm diameter; all xO.35. 



mostly preserved solid, being slightly crushed on parts of the outer 

 side of the whorl. The shell immediately adjacent to the mouth- 

 border is crushed, except for the ventral rostrum which is intact, and 

 the short part of the end of the phragmocone is crushed. The whorl 

 section has a smoothly rounded umbilical wall and edge and an 

 evenly rounded venter. The sides of the whorl converge strongly 

 towards the venter and the greatest whorl breadth is a quarter to a 

 third of the whorl height from the umbilical seam. The venter of the 

 previous whorl can be seen at five breaks in the body-chamber (Fig. 

 3); it is evenly rounded like the venter of the body-chamber, but on 

 the smallest visible cross-section the inner whorl (ie. about 1.8 

 whorls before the mouth-border, at a diameter of approximately 140 

 mm) has a narrower rounded venter and flatter sides, like that of a 

 more compressed Idoceras. Small portions of the final septum are 

 also visible here, attached to the outside of the venter of the inner 

 whorl. The shell is visible at several places on the body-chamber, 

 and is completely smooth, with no trace of any ornament. Measure- 

 ments of CA1034: at 460 mm diameter: 135 (0.29), 97 (0.21), 215 

 (0.47). 



Remarks. This very large body-chamber closely resembles the 

 largest of Venzo's (1959: pi. 7, fig. 2) figured specimens, which is 

 here designated lectotype. That specimen is 280 mm diameter, and 

 appears to be a complete adult macroconch with 0.75 whorls of 

 body-chamber. It has traces of forwardly angled secondary ribs on 

 the venter at the end of the phragmocone, 0.8 whorls before the 

 aperture, and appears to become smooth from the beginning of the 

 body-chamber. The Yemen specimen is almost exactly one whorl 

 larger, the end of its phragmocone being the same size as the mouth- 

 border of the lectotype, so its complete lack of ornament agrees with 

 the lack of ornament on the lectotype at the same size. Up to about 

 150 mm diameter Wocerai hararinum has ribs that are fairly coarse, 

 but typical oi Idoceras. as can be seen on the figured paralectotypes 

 (Venzo, 1959: pi. 6, fig. 8; pi. 7, fig. 3). 



The age of /. hararinum in Ethiopia is a problem: Venzo ( 1959: 

 186, 190) referred it to the Tenuilobatum Zone (covering the whole 

 of the Lower Kimmeridgian), but his distribution tables show that at 

 Diredaua it is associated with many other ammonites, including 

 Pachysphinctes, Katroliceras and Simaspidoceras. If they are all of 



the same age, the present evidence from Yemen suggests that this age 

 cannot be older than the upper half of the Eudoxus Zone and is more 

 probably Beckeri Zone. The other three localities in Ethiopia at 

 which /. hararinum occurs, all of which were referred to the 

 Tenuilobatum Zone by Venzo, do not contain other ammonites from 

 which age evidence can be deduced. Of even more interest at 

 Diredaua is the presence of a single specimen (the holotype) of an 

 ammonite described as Ringsteadia daua Scott (1943: 65, pi. 11, 

 figs 1, 2). Also, two ammonites from Dogou and one from Ganame 

 were made the types of another new species of Ringsteadia. R. 

 africana Scott (1943: 64, pi. 10, figs 1, 2). Scott referred all these 

 specimens to the uppermost Oxfordian, an age assessment that was 

 quoted by Arkell (1956: 314) as giving 'an exceptionally precise 

 correlation with the topmost zone of the Oxfordian of NW Europe'. 

 The Ethiopian 'Ringsteadia' have all the morphological characters 

 of large Idoceras: the holotype of '/?.' africana (Scott, 1943: pi. 10, 

 figs 1 , 2) has secondary ribs forming chevrons on the venter which 

 disappear at about 200 mm diameter, then the whorls are smooth; it 

 is septate to 2 15 mm diameter, and has one quarter of a whorl of body 

 chamber up to 240 mm diameter; it would have been about 300 mm 

 diameter when complete with three-quarters of a whorl of body- 

 chamber. In fact Scott's figure of that holotype bears such a close 

 resemblance to the lectotype of/, hararinum. when compared at the 

 same size, that it is likely that the two ammonites are conspecific. 

 '/?.' daua might also be the same: it is difficult to judge from Scott's 

 figure, but the description of the ornament is like that of Idoceras. 

 Other perisphinctids from the same localities in Ethiopia, especially 

 Perisphinctes vokesi Scott (1943: pi. 10, figs 3, 4) andP. spathi Scott 

 ( 1943: pi. 13, figs 2, 4), could well be examples of Pachysphinctes. 

 or other genera that occur in the top of the Kimmeridgian (Eudoxus 

 and Beckeri Zones) and not earlier. TTiis Ethiopian fauna seems to 

 have placed too low in the zonal sequence. 



Occurrence. Middle part of the Kilya Member, Naifa Cliff; 

 Beckeri Zone, Upper Kimmeridgian. 



Genus NEBRODITES Bmckhardu 1912 



Type SPECIES. Simoceras agrigentinumGemmeWaio, 1872b, sub- 

 sequently designated by Spath (1925: 130). 



Nebrodites hospes (Neumayr, 1873) 



PI. 8, fig. 4 



1873 

 1875 

 1876 



1877 



1877 



1888 

 1888 



1893 

 1905 



Perisphinctes hospes Neumayr: 185, pi. 39, fig. 3. 



Ammonites doublieri d'Orbigny; Favre: 34, pi. 4, fig. 2. 



Ammonites sautieri Fontannes: 294, pi. 16, fig. 1; pi. 17, 



fig. 1 (non pi. 18, fig. 1). 



Ammonites (Perisphinctes) allobrogicus Pillet; Favre: 50, 



pi. 5, fig. 4. 



Ammonites (Simoceras) doublieri d'Orbigny; Favre: 57, pi. 



7, fig. 2 {non fig. 4). 



Ammonites planula Hehl; Quenstedt: 976, pi. 108, fig. 5. 



Ammonites planula /H/Mor Quenstedt: 976, pi. 108, fig. 8. 



Ammonites cf. balderus Oppel; Quenstedt: 978, pi. 108, fig. 



12. 



Hoplites guimaraesi Choffat: 72, pi. 17, fig. 11. 



Simoceras cf. malletianum (Fontannes); Kilian & 



Guebhard:827, pi. 50, fig. 1. 



PLATE 9 



Fig. 1 Idoceras cf. hararinum Venzo, base of middle limestone part of Kilya Member (fauna 7), Naifa Cliff. CAI034, xO.34. 



Fig. 2 Aspidoceras kmnispiiuim (J. de C. Sowerby), base of middle limestone part of Kilya Member (fauna 7), Naifa Cliff. 2a, 2b, CA1036, wholly 



septate. 

 Fig. 3 Aspidoceras upeninniaim Zittel, upper part of middle limestone part of Kilya Member (fauna 7). Wadi Kilya. 3a, 3b, CAl 192, xO.66. 



