UPPER CRETACEOUS AMMONITE 
less importance in Niger, if they are present at all. Their possible 
absence may have allowed populations of P. cauvini in Niger to 
develop a greater range of morphotypes due to lack of 
competition. Meister et al. (1992: 72-76) described a number of 
additional forms from Niger as Vascoceras (Paravascoceras) 
cauvini forme crassum (Furon) and V. (P.) cauvini forme de 
transition entre forme crassum et V. (P.) proprium (Reyment) . 
They are further discussed below under Vascoceras globosum. 
Also of interest in regard to their general whorl proportions 
are Paravascoceras rumeaui Collignon (1957: 122, pl. 16, fig. 2; 
_ Freund & Raab 1969: 21, pl. 3, figs 4, 5; text-figs 6c, d; Luger & 
| Groschke 1989: 380, pl. 41, figs 5, 6; pl. 42, figs 3, 4; text-fig. 8D) 
from Algeria, Egypt and Israel and Vascoceras costellatum 
Collignon & Roman (in Amard et al. 1981: 51, pl. 2, figs 6a, b) 
from Algeria. These species have adult ventral ribbing like that in 
P. cauvini but are more inflated. They may, like the Niger forms, 
be regional variants of P cauvini. Luger & Groéschke (1989: 
375-376) discussed the question of whorl breadth in P cauvini 
but, unlike Schébel (1975), regarded P. rumeaui as distinct from 
P. cauyini. They further separated individuals with depressed 
whorls but which were otherwise similar to P cauvini as 
Vascoceras cf. cauvini (Luger & Gréschke 1989: 376, pl. 42, fig. 2: 
pl. 43, fig. 3; text-figs 6F, 8B). 
The P. cauvini of Collignon & Roman (in Amard et al. 1981: 
51, pl. 3, fig. 9) have whorls only a little broader than high and 
probably belong here. Their Paravascoceras chevalieri (Furon) 
(Collignon & Roman in Amard et al. 1981: 52, pl. 6, figs 1, 2) and 
Nigericeras barcoicense (Choffat) (Collignon & Roman in 
Amard etal. 1981: 54, pl. 4, figs 16a, b) are similar to and may be 
conspecific with P. cauvini. The Paravascoceras aff. chevalieri of 
Reyment (1955: 63, pl. 14, figs 1a, b), however, shows three rows 
of tubercles upon the ventral ribs and more closely resembles 
early Thomasites gongilensis from unit O at Ashaka (see Figs 
41-44). 
The Vascoceras (Paravascoceras) cf. cauvini from Angola 
described by Cooper (1978: 130, figs 6C-H, 35-37) is a 
Nigericeras. 
Berthou et al. (1985: 72) speculated that Vascoceras 
barcoicense Choffat (1898: 67, pl. 17, fig. 1; pl. 22, fig. 5; Berthou 
et al. 1985: 70, pl. 4, figs 1-3) might turn out to be a senior 
synonym of P. cauvini. The strong adult ribbing of the latter 
species is, however, unknown in V. barcoicense. Whorl 
proportions in the two are similar but nothing is known of the 
early growth stages in V. barcoicense. The species may belong in 
Paravascoceras or alternatively it may be an involute, weakly 
ornamented variant of Vascoceras gamai Choffat, according to 
Berthou et al. (1985: 71). 
V. barcoicense exile Cobban, Hook & Kennedy (1989: 47, figs 
47, 87Q-S, 89M-GG) from New Mexico resembles P. cauvini in 
whorl proportions but is more involute. Specimens from low in 
the Pindiga section may be similar in this respect (Fig. 8) but V 
barcoicense exile has a different juvenile ornament of rather 
strong ventral ribs. The V. (V.) cauvini of Kennedy et al. (1989: 
82, figs 9G, 20C-G) from Texas are similar to and probably 
conspecific with V. barcoicense exile. 
| Further involute compressed forms are the Nigericeras 
‘|Jacqueti involutum Meister, Alzouma, Lang & Mathey (1992: 68, 
pl. 4, figs 3-5; text-fig. 14) from Niger. Again, these show 
similarities with P cauvini from unit H at Pindiga but are 
consistently more involute. Their suture pattern (Meister et al. 
1992: fig. 14) is incompletely known but seems to be intermediate 
_|between that of Nigericeras and Paravascoceras. Meister et al. 
'|(1992) regarded N. jacqueti involutum as an offshoot of N. gadeni 
derived through N. jacqueti jacqueti. It may be the product of a 
67 
local lineage independent of that giving rise to P. cauvini. 
Genus PSEUDOVASCOCERAS gen. nov. 
TYPE SPECIES. Vascoceras nigeriense Woods, 1911. 
DIAGNOsIS. Moderately evolute to moderately involute, 
moderately compressed to moderately depressed ammonites. 
Whorls rounded to subpentagonal. Ornament of umbilical, 
inner and outer ventrolateral and siphonal tubercles which may 
be borne upon transverse to concave ribs of varying strength. 
Additional ventral ribs frequently present. Ornamental elements 
of highly variable persistence during ontogeny, sometimes 
extending onto the body-chamber, in other cases confined to the 
earliest growth stages. Suture line simple with evenly frilled 
elements; saddles often elongate and rectangular in outline, 
lateral lobe fairly broad. 
REMARKS. Of all the ammonites from north-eastern Nigeria 
showing ‘vascoceratid’ suture patterns it is the multituberculated 
forms which have proved most problemmatical and which have 
received the most varied taxonomic treatment. This is not 
surprising given the huge range of morphotypes that are 
represented within assemblages from the same stratigraphical 
horizon, at Ashaka unit O. In fact three multituberculated 
genera are present therein, end members of which are not always 
easy to differentiate. Forms attributable to Rubroceras Cobban, 
Hook & Kennedy occur as rarities (Zaborski 1993); a larger 
number of individuals belong in Fikaites Zaborski (1993); but 
the greatest number are here referred to Pseudovascoceras 
nigeriense (Woods). 
In his treatment of this last group Barber (1957) assigned 
them to three genera, Vascoceras, Nigericeras and 
Paramammites Furon, and no less than seven species. The last 
two generic determinations can easily be disposed of. The type 
species of Paramammites (by the subsequent designation of 
Reyment 1954b: 225), Vascoceras polymorphum Pervinquiére 
(1907: 336, pl. 21, figs 2, 6; text-fig. 126) (see also Renz 1982: 
84-85; Chancellor e¢ a/, in press) has a juvenile ornament of 
varying strength, often with large spinose tubercles, but always 
lacks siphonal tubercles. The present material has nothing to do 
with Paramammites. Forms with strong adult costae, interrupted 
ventrally, have often been referred to this genus without 
knowledge of their ontogenetic development (see also Cobban et 
al. 1989: 51; Zaborski 1990b: 574-575) thus creating a rather 
confused situation. Nigericeras resembles the present material in 
only one real respect, the presence of seven rows of tubercles. In 
detail its ornament is more regular and in all genuine members 
of the genus it is confined to the early whorls (see Schneegans 
1943). The suture in Nigericeras, although simple, is of a 
distinctly acanthoceratine pattern, unlike that in the present 
material and other forms mentioned below also previously 
referred to Nigericeras. Nor can the present material be referred 
to Vascoceras. Its ornament is unlike than in any known species 
of the genus and quite distinct from that in the type species V. 
gama. 
Cobban er al. (1989: 51) pointed out that Barber’s (1957) 
Paramammites needed a new generic name. They suggested that 
these forms were in part ribbed and tuberculated derivatives of 
Vascoceras. The genus Pseudovascoceras is here proposed to 
include this material, the name alluding to the homeomorphy 
between smooth members of the type species and true 
Vascoceras. The origin of the genus, however, is thought to lie in 
