76 



M.K. HOWARTH 



Family SIMOCERATIDAE Spath, 1924a 

 Genus PSEUDOCLAMBITES Spath, 1925 



Type species. Pseudoclambites aenigmaticus Spath, 1925, by 

 monotypy. 



Remarks. This genus was created by Spath (1925: 149) for six 

 poorly preserved ammonites from Bihendula, Somalia. Their hori- 

 zon was not well recorded, but from other ammonites with which 

 they were probably associated he surmised that their age was 

 Tithonian or younger. Spath was unsure of the affinites of 

 Pseudoclambites: although he included the genus in the Berriasellidae 

 as 'incertae sedis", he also discussed its alternative inclusion in the 

 Simoceratidae or the Virgatosphinctinae (as a development of 

 Anavirgatites), but did not consider that it could belong to the 

 Spiticeratinae (with Pwniceras) on account of the different form of 

 its constrictions. Later, another specimen from near Bihendula, 

 described as the new species Pseudoclambites costatus Spath (1935: 

 214), allowed Spath to definitely place the genus in the Simoceratidae, 

 and from the other ammonites with which it was associated in the 

 Gawan Limestone, he could determine its age as Tithonian with 

 more certainty. 



The holotype of the new Yemeni species described below is much 

 better than any of the material available to Spath. Its has the same 

 morphological features as Spath's genus, differing only slightly in 

 whorl proportions and details of ribbing, which are not worth more 

 than species distinction. The features that led Spath to place the 

 genus in the Simoceratidae seem to be confirmed by the material 

 from Wadi Arus: the passage of the ribs onto the venter without 

 projection forwards, the broad, shallow ventral sulcus, and especi- 

 ally the constrictions that are parallel with the ribs behind, instead of 

 cutting across the ribs behind at a more prorsiradiate angle, as is 

 characteristic of Spiticeratinae. Nevertheless, the resemblance 

 between Pseudoclambites and some species of Pwniceras, means 

 that consideration should be given to a possible origin of the 

 Spiticeratinae (as the earliest subfamily of the Olcostephanidae) in 

 the Simoceratidae. The date of Pseudoclambites in the Microcanthum 

 Zone at the base of the Upper Tithonian in Yemen, also vindicates 

 Spath's ideas of the date of the Somali material. 



Pseudoclambites araense sp. no v. 



Derivation of name. After Wadi Arus. 



PI. 16, figs 1,3 



Holotype. CA747 from the microbialite boulders, 6 m above the 

 base of the Arus Member in the east cliff of Wadi Arus. 



Paratypes. Three specimens, CA748-50, all from the same lo- 

 cality and horizon as the holotype. 



Other material. Fragments of 13 specimens (CA752-64) from 

 the same horizon and locality as the holotype, and a fragment of a 

 very large specimen (CA75 1 ) from the same horizon in the west cliff 

 in Wadi Arus. 



Diagnosis. Evolute, slightly compressed whorls, with a broad, 

 shallow sulcus in the middle of a flat venter. Ribs sharp, prorsiradiate 



and bifurcafing on inner whorls, fading to leave outer whorls smooth 

 except for clavi at the umbilical edge. 



Description. The holotype is the only specimen that is well 

 preserved; all the others are fragments and most have rough eroded, 

 surfaces. The holotype has a possibly complete and adult aperture at 

 104 mm diameter, and its final septum is exactly one whorl before 

 the aperture; its measurements are: at 97.5 mm diameter: 31.5 

 (0.32), 26.8 (0.28), 40.7 (0.43).The largest paratype (CA749) is 240 

 mm diameter, in three large pieces, and has traces of septa up to a 

 diameter of about 1 25 mm at 1 .2 whorls before the aperture, but 

 none are visible on the final whorl. The second paratype (CA748) is 

 a complete ammonite 121 mm diameter, but it is very roughly 

 preserved and septa and suture-lines are not visible. The third 

 paratype (CA750) is part of a body-chamber about one-third of a 

 whorl long and 1 20 mm diameter; it is uncrushed, has parts of the 

 inner whorls attached and is very similar to the holotype; at a whorl 

 height of 34 mm, the whorl breadth is 29.5 mm. The other 13 

 specimens are fragments of phragmocones and body-chambers, 

 including (CA75 1 ) part of a large smooth body-chamber at about 

 200 mm diameter. 



The whorls are evolute and slightly compressed, with a rounded 

 umbilical edge, whorl sides that converge to a smoothly rounded 

 ventro-lateral area, then a flat venter with a broad, shallow sulcus in 

 the middle. Ribs on the inner whorls are sharp and prorsiradiate, then 

 become raised into radial clavi at the umbilical edge and much 

 reduced on the middle and outer part of the whorl from about 60 mm 

 diameter; they then gradually disappear leaving the clavi, which 

 become more widely spaced and nodular. There are two or three 

 secondary ribs for each primary rib, which appear on the outer part 

 of the whorl by indisfinct division of the primaries or by intercala- 

 tion. The ribs pass onto the venter radially without any forwards 

 inclination, and there is a broad, very shallow, smooth sulcus in the 

 middle of the venter. There are 4 or 5 narrow constrictions per whorl, 

 following the line of the primary ribs exactly. At large sizes the ribs 

 tend to be further effaced, leaving only umbilical clavi, traces of the 

 secondary ribs at the sides of the venter, and occasional constric- 

 tions. Details of suture-lines are not visible. 



Remarks. P. araense is characterized by Perisphinctid-like inner 

 whorls, which become progressively smoother from 60 mm diameter, 

 umbilical edge clavi, and a shallow ventral sulcus that is exactly the 

 same as in Spath's Somali material. It is slightly more evolute, has 

 more compressed whorls and probably a higher rib-density on the 

 inner whorls than P. aenigmaticum. P. costatum Spath has stronger, 

 more widely spaced ribs, and no clavi at the umbilical edge. Despite 

 its Simoceratid features, P. araense has considerable similarities 

 with Spiticeras (Negreliceras) singulare Leanza (1945: 79, pi. 15, 

 figs 1. 6; pi. 17, figs 1, 6, 7, 9) (especially pi. 17 fig. 1), which is 

 accepted as an Upper Berriasian species of Spiticeras in Argentina 

 by Leanza (1981b: 570). 



Occurrence. Microbialite boulders, Arus Member, Hajar For- 

 mation, Wadi Arus; Microcanthum Zone, Upper Tithonian. 



PLATE 16 



Figs 1, 3 Pseudoclambites araense sp. nov., microbialite boulders, Anis Member (fauna 9), east cliff, Wadi Arus. la, lb, holotype, CA747; 3a, 3b, 



paratype, CA750, body-chamber 

 Fig. 2 Virgatosimoceras broilli (Schneid), microbialite boulders, Arus Member (fauna 9), west cliff, Wadi Arus. 2a, 2b, CA767. 

 Fig. 4 Spiticeras (Spiticeras) suhspitiense (Uhlig), bed 34, Mintaq Member (fauna 13), Mintaq Salt Dome. 4a, 4b, CA597, body-chamber 

 Fig. 5 Spiticeras (Negreliceras) paranegreli Djanelidze, bed 31. Mintaq Member (fauna 13). Mintaq Salt Dome. 5a, 5b, CA607. 

 Fig. 6 Spiticeras pricei sp. nov., bed 60, Mintaq Member (fauna 13), Mintaq Salt Dome. 6a, 6b, paratype, CA630. 



