78 
and dense ribbing style of V. bullatum with the whorl 
proportions and suture pattern of V. globosum costatum. 
Material of this kind has not been found in the present study and 
its precise affinities are uncertain. 
Vascoceras rumeaui Collignon (1957) has an ornament of 
strong ribs similar to that in V. bullatum but is less depressed. As 
discussed above, it may be more closely related to Paravascoceras 
cauvini. V. durandi Choffat and the doubtfully distinct V 
kossmati Choffat (see Berthou et al. 1985 for a review) are both 
depressed, relatively evolute species but lack the marked ribbing 
and adult apertural modifications seen in V. bullatum. 
Vascoceras globosum (Reyment, 19545) 
REMARKS. This species was discussed by Kennedy et al. (1987: 
46). They brought into synonymy a large amount of material 
described from Nigeria and elsewhere including 
Pachyvascoceras — globosum Reyment (19545) and 
Pachyvascoceras proprium Reyment (19545) under the name 
Vascoceras proprium (Reyment, 19546). Barber (1957: 21-27), 
however, had already treated the above two forms as conspecific 
and selected Vascoceras globosum (Reyment, 19545) as the 
species name. V. globosum accordingly has priority over V. 
proprium and should replace it. Nigerian specimens assigned to 
the species are here referred to three subspecies as detailed below. 
The V. globosum group shows a wide morphological variation 
and complex phylogenetic relationships. Early members of the 
group seem to include the ancestors of Thomasites gongilensis 
(Woods). Later members are characterized by rather complex 
sutures; V. obscurum and probably also Neoptychites Kossmat 
were derivatives. 
The precise origin of V. globosum is obscure. There are no 
obvious ancestors within the north-eastern Nigerian sections. V. 
woodsi is a possibility but is more evolute and has a stronger, 
more persistent juvenile ornamentation. Paravascoceras cauvini 
is markedly more compressed while the inner whorls of its later 
members are entirely smooth, unlike those in V. globosum 
costatum. 
Berthou et al. (1985: 72) suggested that Vascoceras 
(Pachyvascoceras ) crassus Furon, 1935 was a senior synonym of 
Pachyvascoceras costatum Reyment, 1954b (= V. globosum 
costatum). Meister et al. (1992: 72, pl. 7, figs 1, 2, 4, 5) described 
formes from sections at Tanout Aviation and Birgimari in Niger 
as Paravascoceras cauvini of V. crassum type and others 
transitional from V. crassum to V. proprium type. The latter 
group could probably include their V. gr. ellipticum Barber 
(Meister et al. 1992: 76, pl. 7, fig. 3; pl. 8, figs 1, 2) from the same 
sections. These formes are associated with Paravascoceras 
cauvini of typical aspect. Schneegans (1943) also reported 
passage forms from P. cauvini to V. crassum in Niger. Meister et 
al. (1992: 74) discussed the possible relationships within the 
Niger faunas. They remarked that undoubted V. proprium (= V. 
globosum) had not been found in Niger, and speculated that the 
horizons with P cauvini contained essentially monospecific 
ammonite faunas; this species produced a wide range of 
morphotypes with variable degrees of whorl compression and 
ornamental strength. According to this interpretation V 
crassum is a homeomorph of V. globosum costatum, the first a 
member of the P cauvini group, the latter having a separate 
origin. In support it may be noted that unit O at Ashaka, in 
which V. globosum appears, also contains the abrupt first 
occurrences of V. bullatum and Pseudovascoceras nigeriense. The 
base of unit O is a marine flooding surface suggesting that its 
fauna is largely an introduced one, the ancestors of which lie 
P.M.P. ZABORSKI 
outside north-eastern Nigeria. Vascoceras (Pachyvascoceras) 
crassum and V. globosum are here regarded as distinct from one 
another; the former, as stated above, is probably best referred to 
Paravascoceras. 
Vascoceras globosum costatum (Reyment, 1954b) 
Figs 38-40, 50 
Pachyvascoceras costatum Reyment: 257, pl. 3, fig. 6; 
pl. 4, fig. 3; pl. 5, fig. 2; text-figs 3a, b, 5. 
1955 Pachyvascoceras costatum Reyment; Reyment: 65, pl. 
19546 
14, figs 2, 4. 
21957 Vascoceras robustum Barber: 15, pl. 5, fig. 1; pl. 26, figs 
5, 6: 
1957 Vascoceras polygonum Barber: 17, pl. 5, fig. 2; pl. 29, 
figs 1-3. 
1957 Paravascoceras costatum costatum (Reyment) Barber: 
35, pl. 14, fig. 1; pl. 32, figs 1-3. 
1957 Paravascoceras costatum quadratum Barber: 35, pl. 16, 
fig. 2; pl. 32, figs 10, 11. 
1957  Paravascoceras costatum tectiforme Barber: 37, pl. 14, 
fig. 4; pl. 15, figs 1, 3; pl. 16, fig. 2; pl. 32, figs 4-7. / 
1965  Pachyvascoceras costatum Reyment; Reyment: pl. 3, 
fig. 17. 
1976 Vascoceras robustum Barber; Offodile & Reyment: 54, 
figs 23a, b. 
1976 —-Vascoceras ellipticum Barber; Offodile & Reyment: 55, 
figs 25a, b. 
1976  Paravascoceras costatum (Reyment); Offodile & 
Reyment: 55, figs 26a, b. 
1976  Paravascoceras  tectiforme 
Reyment: 55, figs 29a, b. 
1989  Paravascoceras tectiforme Barber; Meister: 21, pl. 7, 
figs 1, 2; pl. 8, figs 1—S; text-fig. 13. 
1992 Vascoceras tectiforme (Barber) 
Courville: pl. 7, figs 1, 2. 
Barber; Offodile & 
sensu. Meister; 
MATERIAL AND OCCURRENCE. Twenty-six specimens, C.93310, | 
C.93519-34, C.93535a—d, C.93536a-e, Pindiga Formation, unit | 
O, Ashaka. | 
DIMENSIONS. See Figs 12, 48. 
REMARKS. The phragmocone in V. globosum costatum reaches a 
diameter in excess of 130 mm, making it the largest member of | 
the genus known in north-eastern Nigeria. Whorl breadth is | 
slightly to distinctly greater than whorl height while the | 
umbilicus represents 15-28% of the total diameter. In overall 
shell proportions V. globosum costatum overlaps with V. bullatum 
and Pseudovascoceras nigeriense and smoother individuals of | 
these two species may be difficult to distinguish from it, 
especially in their middle growth stages. 
At diameters of less than 30 mm (Figs 39, 40) the whorls in V. 
globosum costatum are weakly ornamented. Some forms are | 
virtually smooth, others display umbilical tubercles but most 
commonly there are weak, broadly rounded ribs, most | 
pronounced ventrally and sometimes with traces of bullate | 
ventrolateral tubercles. The whorls tend to be more compressed | 
in the early than in the later growth stages. 
In the middle whorls ornament may be lacking or there may be | 
broad, low ventral ribs. Umbilical tubercles persist in some | 
individuals. In the adult stages irregular fold-like ribs may 
appear, especially upon the venter. The range of shell shapes and | 
ornamentation is well displayed by the abundant previously 
described material (see synonymy list). 
