14 
Annals of the Transvaal Museum 
is very slightly concave forwards on the middle of the external surface, the 
concavity being so slight, that one is sometimes in doubt, whether to regard 
the mouth-edge here as straight or not. The mouth-edges appear as grooves 
on the cast and as very slight ridges on the shell. There are six old mouth- 
edges on the last whorl of the type. 
The lobe-line resembles very much that of J etvagonites Cola Forbes sp. 
The external saddle is the largest. The external lobe is of the same length or 
perhaps slightly longer than the first lateral lobe. The second lateral lobe 
reaches nearly as far backwards as the first. The three principal saddles are 
trifid. The two incisions in the anterior portion of 
the external saddle have practically the same 
length. In the first lateral saddle the external of 
the two incisions is longer than the internal one 
and in the second lateral saddle the internal in- 
cision lies nearer to the middle of the front of the 
saddle than the external one. The first lateral lobe 
is symmetrically bifid. The second lateral lobe may 
also be called bifid, but it is not symmetrical, for 
the secondary saddle at the base of the lobe is 
directed strongly inwards. The second lateral saddle 
lies completely external to the umbilical edge, 
which just touches the external side of the first auxiliary saddle. The 
auxiliaries are very small. There are four auxiliary lobes and saddles, the 
last auxiliary lobe and saddle being mere undulations of the lobe-line. A 
contour line over the posterior ends of the lobes is fairly straight and its 
umbilical portion does not run backwards. A contour line over the anterior 
ends of the saddles, however, is not straight, because its whole portion internal 
to the first lateral saddle bends backwards on its outer portion. 
The above is the description of the lobe-line of the type on a radius of 
1 3 *7 mm. The smallest specimen present shows its lobe-lines beautifully and 
one of them, on a radius of 5 mm. has been chosen for comparison. The ex- 
ternal lobe of this lobe-line is longer than the first lateral lobe, the length of 
the latter being about three-quarters of that of the former. The external saddle 
is symmetrically trifid. The anterior border of the first lateral saddle shows 
two slight indentations, of which the external one is deeper than the other. 
The anterior border of the second lateral saddle is more or less evenly rounded. 
The umbilical portion of the lobe-line shows three small saddles, which are 
really nothing more than slight undulations. The two lateral lobes are bifid 
and the secondary saddle at the base of the second lateral lobe is placed un- 
symmetrically. At a radius of less than 3 mm. there is only one auxiliary 
undulation (saddle). 
Diameter ... 
Type 
37-6 mm. (i-oo) 
Paratype No. i 
25-5 mm. (i-oo) 
Paratype No. 2 
15 mm. (i-oo) 
Height of last whorl 
14 
. (0-37) 
9 
(0-35) 
5-6 „ 
(0-37) 
Thickness of last whorl . . . 
15-4 L 
. (0-41) 
10-2 „ 
(0-40) 
6 
(0-40) 
Height of penult, whorl ... 
7 
, (0-19) 
4-5 
(o-i8) 
2-8 „ 
(0-19) 
Thickness of penult, whorl 
7-6 , 
, (0-20) 
5 
(0-20) 
3 
(0-20) 
Diameter of umbilicus ... 
15*5 , 
, (0-41) 
10-6 ,, 
(0-42) 
6-2 „ 
(0-41) 
Paratype No. 2 has suffered from pressure. 
T etvagonites nupevus belongs to the group of Tetragonites Cala Forbes sp. 
It is easily distinguished from this species through the following characters: 
T. Cala has whorls of trapezoidal section; its involution is about one-seventh; 
Text-fig. 8. Tetragonites 
nupevus. Lobe-line of 
type up to the umbilical 
suture on a radius of 
13 mm, X3. 
