AMMONITES AND NAUTILOIDS OF WADI HAJAR 



49 



1959 Katroliceras katmlense (Waagen); Collignon; pi. 122, fig. 



458. 

 1984 Katroliceras pottingeri (J. de C. Sowerby): Verma & 



Westermann: 42, text-fig. 5; pi. 4, fig. 1. 



Material. One specimen, CAl 137, fi-om the upper marly part of 

 the Kilya Member in Wadi Kilya. 



Description. The single specimen is partly crushed, about 80 

 mm diameter, and has the middle part of the final whorl missing. At 

 the aperture, part of the mouth-border can be seen where the shell 

 thickness wedges out to nothing, and small portions of a suture-line 

 are visible 290° earlier. The marked modification of the final three 

 ribs and the contraction of the whorl breadth at the aperture suggest 

 that it is an almost fully grown adult microconch, though there is no 

 trace of a lappet. Primary and secondary ribs are coarse on the inner 

 whorls, and become noticeably more widely spaced on the final 

 quarter whorl, where the venter becomes broad and the whorl 

 section depressed. 



Remarks. This probable near-complete adult microconch has 

 much more coarsely ribbed inner whorls and is more depressed at 

 the aperture than any of the specimens of Katroliceras formosum in 

 the same bed in Wadi Kilya. It is closely similar to the best example 

 of K. pottingeri figured previously, ie. Futterer's Mombasa speci- 

 men, which was splendidly refigured by Spath (1931: pi. 102, figs 

 5a, 5b - not figs 5c, 5d, which probably belongs to a different 

 specimen), and reproduced in the Treatise (Arkell, 1957, fig. 425). 

 Spath's figure appears to show the base of a lappet in the aperture, so 

 it is an adult microconch complete at 85 mm diameter. The Yemeni 

 specimen is a little smaller, and is slightly short of its final adult size. 

 Compared with these, the Cutch holotype of Katroliceras pottingeri, 

 refigured by Verma & Westermann (1984: 43, text-fig. 5), is very 

 poorly preserved, and it is impossible to see suture-lines or judge its 

 degree of completeness. 



Occurrence. Upper marly part of the Kilya Member, Naifa 

 Formation, Wadi Kilya: Hybonotum Zone, Lower Tithonian. 



Katroliceras sp. indet. 



Fragments of about 45 specimens (including CAl 138^4), all too 

 fragmentary or too poorly preserved to be specifically identified, 

 were obtained from the upper marly part of the Kilya Member in 

 Wadi Arus. They could be examples of either K. formosum or K. 

 pottingeri. 



Genus SUBDICHOTOMOCERAS Spath, 1925 

 Type SPECIES. Subdichotomoceras lamplughi Spath, 1925. 



Subdichotomoceras llatissimum (Zwierzycki, 1914) 



PI. 2, fig. 5 



71914 Perisphinctes latissimus Zwierzycki: 65, pi. 8, fig. 4. 

 71931 Subdichotomoceras inversum Spath: 521, pi. 84, fig. 7; pi. 



85, fig. 4. 

 71931 Subdichotomoceras simplex Spath: 522, pi. 83, fig. 8. 

 71933 Perisphinctes cf. sparsiplicatusV^a.agen;Diclhch: 20, pi. 1, 



fig. 2. 



7 1 959 Subdichotomoceras diudema Spath; Collignon: pi. 1 48, fig. 



591. 

 71959 Subdichotomoceras mandaranense CoWignon: pi. 149, figs 



597, 7598, 7599. 

 1984 Subdichotomoceras aff. sparsiplicaium (Waagen); Verma 



& Westermann: 47, pi. 5, fig. 1. 



Material. One specimen, CAl 145, from the upper marly part of 

 the Kilya Member in Wadi Kilya. 



Description. This is a well-preserved microconch consisting of 

 half a whorl of uncrushed body-chamber ending at an adult mouth- 

 border at 60 mm diameter. The whorl is evolute, and the whorl 

 section slightly depressed as shown by the measurements below: 

 those at 59 mm diameter were taken inside the collar immediately 

 before the aperture, and the low values for whorl height and whorl 

 breadth reflect the depth of that constriction, while those at 55.5 mm 

 (where Wh and Wb are higher) are between the two major primary 

 ribs before the constriction and give a better value of the depression 

 of the whorl section. The strong, sharp primary ribs are regularly 

 biplicate at the rounded ventro-lateral angle, except for a single rib 

 angled more strongly forwards immediately before the final con- 

 striction. The secondary ribs are curved gently forwards on the 

 venter without interruption. At the aperture a strong rib follows the 

 constriction, then the shell is flared, and small portions of the mouth- 

 border itself are preserved near the umbilicus and the mid- venter, but 

 unfortuntely not on the side of the whorl where a lappet would be 

 expected. 



Measurements 



D Wh 



CAl 145 59.0 15.3(0.26) 



CAl 145 55.5 15.6(0.28) 



CAl 145 43.0 11.8(0.27) 



Wb U WhAVb 



16.4(0.28) 31.4(0.53) 0.93 



18.6(0.34) 29.5(0.53) 0.84 

 15.0(0.35) — 0.79 



Remarks. Most species and most figured specimens of 

 Subdichotomoceras are more depressed than this Yemeni specimen, 

 and it is difficult to find examples that are sufficiently evolute and 

 have similar whorl proportions at the same diameter (ie. a whorl 

 height/breadth ratio of 0.79-0.84 at 43-55 mm diameter). Thus one 

 of the commonest Cutch species, S. sparsiplicatus (Waagen, 1875: 

 204, pi. 49, fig. 2; revised by Spath, 1931: 523, pi. 86, fig. 7; pi. 87, 

 fig. 4; pi. 101, fig. 1) is consistently too depressed (WhAVb ratio of 

 0.67-0.7 at 70-86 mm diameter), though the ribbing is similar. 

 There is little doubt that the highly evolute specimen from the 

 Hybonotum Zone at Mombassa figured by Verma & Westermann 

 (1984: pi. 5, fig. 1 ) as 5. aff. sparsiplicatum (Waagen) (WhAVb ratio 

 0.89 at 1 14 mm diameter), belongs to the same species. Said to be 

 almost complete at 114 mm diameter, with the mouth-border just 

 missing, it is probably a microconch, especially when compared 

 with macroconchs of Subdichotomoceras (eg. S. aff. sparsiplicatum 

 (Waagen) of Verma & Westermann, 1984: pi. 6, fig. 3; pi. 7, figs 1, 

 2) that are larger, more involute and have higher whorls. Most 

 Subdichotomoceras from the Lower Tithonian of Madagascar 

 (Collignon, 1959: pis 148, 149, figs 591-599) are too involute or too 

 depressed, though two (figs 591, 597) might be the same as the 

 Yemeni specimen. Instead of proposing a new species based on only 

 the Yemeni and the Verma & Westermann (1984: pi. 5, fig. 1) 

 specimens, it seems better to identify them with S. latissimus 



PLATE 4 



Figs 1-3, 5 Katroliceras formosum Spath, upper marly part of Kilya Member (fauna 8), Wadi Kilya. la, lb, CAl 108: 2A, 2b, CAl 106, wholly septate; 



3a, 3b, CAl 109; 5a, 5b, CAl 107. 

 Fig. 4 Sutneria weidmanni Zeiss. Breadloaf Concretions, Kilya Member (fauna 7), east cliff. Wadi Arus. 4a-4d, SM F.12162; 4a. 4b. xl; 4c. 4d, x3. 

 Fig. 6 Katroliceras pottingeri (J. de C. Sowerby). upper marly part of Kilya Member (fauna 8). Wadi Kilya. 6a, 6b, CAl 137. 



