50 



M.K. HOWARTH 



(Zwierzycki, 1914: 65, pi. 8, fig. 4), from the Lower Tithonian of 

 Tendaguru, Tanzania. Zwierzycki's only figured specimen is simi- 

 larly evolute and has the same pattern and density of ribs, but is only 

 33 mm maximum diameter, and has depressed whorls with a WhAVb 

 ratio of 0.61 at 30 mm diameter. Another small example was figured 

 by Dietrich ( 1 933: pi. 1 , fig. 2), who recorded several others from the 

 Smeel and Nerinella Beds at Tendaguru. Many ammonites (includ- 

 ing Subdichotomoceras) become less depressed at larger sizes, so 

 the same species might be represented at Cutch by the two much 

 larger specimens given the names S. inversum and S. simplex by 

 Spath (1931: pi. 83, fig. 8; pi. 84, fig. 7; pi. 85, fig. 4). They have 

 quadrate, only slightly depressed whorls (WhAVb ratio of 0.87-0.90 

 at 105-120 mm diameter), the same sharp regularly biplicate ribs, 

 and both appear to be macroconchs. Whatever specific name is given 

 to these ammonites from Yemen, Cutch, Mombasa, Tendaguru and 

 Madagascar, they are all from the Hybonotum Zone and are good 

 evidence for the age of the beds in which they occur. 



Occurrence. Upper marly part of Kilya Member, Naifa Forma- 

 tion, Wadi Kilya; Hybonotum Zone, Lower Tithonian. 



Genus SVTNERIA Zittel, 1884 



Type species. Nautilus platynotiis Reinecke, 1818. 



Synonym. EnosphinctesS,c\(inde'f^o\i, 1925; type species, S'Mmer/'a 

 subeumela Schneid, 1914. 



Sutneria weidmanni Zeiss, 1979 PI. 2, fig. 4; PI. 4, fig. 4 



\919Sutneria weidmanni Zeiss: 271, abb. 3, figs 19, 20; abb. 4. 



Material. Seven specimens, CA721-25 and SM F. 12162, 

 F. 12163, from the Breadloaf Concretions in the Kilya Member, east 

 side of Wadi Arus. 



Description. Five specimens have parts of their adult mouth- 

 borders preserved at 24.7, 22.0, 21.0, 19.0 and 17.0 mm diameter, 

 including lappets in four of them; the other two are small inner 

 whorls of 1 1.5 mm and 10 mm diameter, the latter being so highly 

 depressed and cadicone that it is only doubtfully referred loSutneria. 

 There is a marked constricfion, especially in whorl breadth, imme- 

 diately before the mouth-border, then a flared rostrum on the venter 

 and small, triangular, pointed lappets on the side of the whorl; the 

 length of the lappet is approximately half the whorl height. The adult 

 body-chambers are 0.6-0.8 whorls long. The whorls are involute 

 and depressed (WhAVb = 0.81-0.94 at 15-23 mm diameter), and the 

 whorl section is smoothly rounded with no angles at umbilical or 

 ventro-lateral edges. The ornament consists of straight, near-radial 

 primary ribs that divide at the middle of the whorl side into two or 

 three secondaries; occasional ribs on the inner whorls divide into 

 four or five secondaries, and such multiple divisions are usually 

 achieved by successive bifurcations. There are 14-15 primary ribs 

 per whorl at 15-17 mm diameter. A small mid-lateral tubercle, 

 sometimes elongated radially, occurs at some of the primary bifurca- 

 tion points. The ribs tend to fade just before the adult mouth-border. 



Measurements 



D Wh Wb U 



SMF12162 15.3 6.4(0.42) 7.6(0.50) 4.4(0.29) 



SMF12163 16.7 7.3(0.44) 7.8(0.47) 4.4(0.26) 



CA721 23.3 8.9(0.38) 10.7(0.46) 6.3(0.27) 



CA722 20.6 8.1(0.39) 9.8(0.48) 5,6(0.27) 



CA723 20.1 7.9(0.39) 9.7(0.48) 6.1(0.30) 



Remarks. Sutneria weidmanni Zeiss was based on two speci- 



mens from Ali Sabieh, Djibouti, found in association with ammo- 

 nites determined by Prof Dr A. Zeiss (in Conrad. Peybemes & 

 Weidmann, 1975: 19) as Aspidoceras freneixae Collignon. A. 

 bertucati Collignon, Pachyplamdites (?) cf irregularis Spath and 

 Subplanites aff. spathi Venzo. The age was given as Eudoxus Zone 

 (ie. the upper halfofZeiss's (197 1:536. table 1; 1979: 276) 'Middle 

 Kimmeridgian'). The Yemeni specimens are a close match for 

 Zeiss's(1979: abb. 3, figs 19, 20) holotype, and the best preserved of 

 them (PL 4, fig. 4) has a complete mouth-border with lappet on one 

 side. In fact four of the Yemeni specimens have lappets, which are 

 not preserved in either of the Djibouti originals, and they show that 

 the size range of complete adults was at least 17-25 mm diameter. 

 Sutneria weidmanni is somewhat more involute and has more de- 

 pressed and thicker whorls than many species of Sutneria. It is 

 characterized by its thick depressed whorls and its birfurcafing to 

 quadrifurcating primary ribs that bend only gently backwards on the 

 outer half of the whorl side. It is a species of the group leading to S. 

 subeumela Schneid that has been referred to the subgenus S. 

 ffnoj/j/z/ncfeij by some authors (Geyer, 1963: 189; 1969: 65, fig. 1). 



Occurrence. Lower part of Kilya Member, Naifa Formation, 

 east side of Wadi Arus; Beckeri Zone, Upper Kimmeridgian. 



Genus PACHYSPHINCTES Dietrich. 1925 



Type species. Perisphinctes (Pachysphinctes) africogermanus 

 Dietrich, 1925, subsequently designated by Spath (1930: 42). 



Remarks. Pachysphinctes is an East African - Indian Ocean 

 genus, characterized by evolute, square to massive whorls and 

 strong ribs. Species have been recorded and described from Tanza- 

 nia by Muller (1900), Zwierzycki ( 1914) and Dietrich (1925; 1933), 

 from Kenya by Futterer (1894), Spath (1930) and Verma & 

 Westermann (1984), from Ethiopia by Venzo (1959) and Zeiss 

 (1 97 1 ). from Somalia by Spath ( 1 925; 1935). from Cutch by Waagen 

 ( 1 875 ) and Spath (1931), and from Madagascar by Collignon ( 1 959). 

 Some species attain very large sizes and have massive final whorls - 

 a Pachysphinctes muelleri (Burckhardt) (BMHN collection) col- 

 lected by the author and Dr Noel Morris in 1965 in the Mandawa 

 anticline in southern Tanzania is 1095 mm diameter and has a very 

 massive, but incomplete, body-chamber with the following meas- 

 urements: at 1095 mm diameter: 330 (0.30), 320 (0.29). 498 (0.46). 

 While that specimen must be a macroconch. some of the largest 

 known microconchs also occur in Pachysphinctes, eg. those from 

 Cutch figured by Spath ( 193 1 : pi. 77, fig. 1 ; pi. 97, fig. 1 ; pi. 98, fig. 

 5 ) which are 1 65 mm and 1 75 mm diameter at their lappetted mouth- 

 borders. Some of the species in East Africa were revised by Verma & 

 Westermann (1984: 37-41) who examined the type material of the 

 type species, P. africogermanus from southern Tanzania, and desig- 

 nated the 75 mm diameter original of Dietrich ( 1 925 : pi . 1 , fig. 2 ) as 

 lectotype. They (Verma & Westermann, 1984: 39^1, text-fig. 4) 

 also refigured the largest of Futterer's (1894: pi. 2, fig. 1) figured 

 syntypes of P. beyrichi from Mombasa (this is not the lectotype as 

 Verma & Westermann stated, because the smaller original of Futterer, 

 1894, pi. 2, fig, 2, had already been designated lectotype by Spath 

 ( 1 930: 55 )). Both these EastAfrican species have fairly fine, biplicate 

 ribs, and whorls that appear to become massive at large sizes. An 

 even more finely ribbed species from Tanzania is P. mahokondo- 

 beyrichi (Dietrich, 1925: 13, pi. 3, fig. 5). 



Specimens similar to, or identical with, P. beyrichi occur com- 

 monly in Cutch. where a second species is more evolute. has massive 

 depressed whorls, and coarser ribs. Waagen (1875: 191-193) pointed 

 out the difficulties in distinguishing between the two at small sizes. 



