12 
Annals of the Transvaal Museum 
no demarcation between the external surface and the flanks, the section of the 
whorl, through flanks and external surface being practically circular. The high 
umbilical surface is nearly vertical to the plane of symmetry, being very 
steeply inclined towards the centre. There is no sharp line of demarcation 
between the umbilical surface and the flank, the surface between the two being 
only strongly convex. Involution nearly two-thirds. 
The ornamentation of the shell is very delicate. Practically it is smooth 
and only covered by growth-lines. With the magnifying glass these growth- 
lines appear to consist of extremely fine grooves and broad, very low growth- 
ridges. The grooves are separated by much broader interspaces. This orna- 
mentation is most conspicuous on the umbilical surface, diminishes on the 
flanks and has nearly disappeared on the external surface. This may have 
been caused by weathering, for there is practically no difference between the 
outer surface and the umbilical surface of the paratype. Broader and deeper 
grooves, which lie fairly close together, cross the shell at irregular intervals. 
These grooves, separated by the broad interspaces, give the shell, especially 
on the flanks, a banded appearance, which was accentuated by a difference in 
colour when the shell had just been cleaned from matrix. After a few days, 
however, this difference in colour had disappeared. The grooves are nearly 
perpendicular to the umbilical suture, leaning only slightly backwards. Above 
the middle of the umbilical surface they bend forwards and they pass over the 
umbilical edge in a strongly forward direction. However, as soon as they are 
on the flanks, they bend slightly backwards, in such a way, that they are 
slightly concave backwards and still retain a slightly forward direction. On 
the flanks they are practically straight, but on nearing the external surface 
they again become slightly concave backwards, while they are slightly concave 
forwards on the middle of the external surface. 
Spiral ridges have not been seen in the type, and old mouth-edges could 
not be found. However, there are indications of spiral ridges on the paratype, 
and the sipho of this specimen causes a distinct siphonal ridge. 
The lobe-line very much resembles that of Tetvagonites epigonus Kossmat. 
It is, however, even more complicated and the lobes are narrower than those 
of the mentioned species. The saddles diminish in size from the external one 
inwards. The umbilical portion of the lobe-line runs backwards. In Tetvagonites 
Text-fig. 7. Tetvagonites vivgulatus. Lobe-line of type up to the umbilical suture 
on a radius of 16 mm. x 3*5. 
epigonus this running backwards of the lobe-line starts somewhat further out- 
wards. The external saddle and both lateral saddles are practically trifid. All 
lobes up to the first auxiliary reach equally far backwards. The second and 
third auxiliary lobes reach nearly as far backwards as the others. The first 
