Annals of the Transvaal Museum 145 
tubercle. Sometimes the edge of the tubercle is continuous with one rib, 
while another rib begins at each of its sides. Again, one rib is continuous with 
the edge of the tubercle, while another emanates from one side and two from 
the other. Sometimes the edge of the tubercle ends in a groove between two 
ribs. Now and then one of the ribs starts independently of any tubercle at 
the extreme edge of the umbilicus. Now and then, by no means at regular 
intervals, a short rib is intercalated between two others; these short ribs 
start at about the middle of the flank and behave further as the others. At 
irregular intervals the whorl is traversed obliquely by a deep groove, which is 
bordered behind by a thick ridge and in front by a narrow ridge. Its course 
is sinuous, being slightly convex forwards near its inner end, concave forwards 
near its middle and convex forwards at its outer end and on the external 
surface. The ridge in front of the groove starts on the umbilical surface, just 
inside the umbilical edge and passes on to the flank without forming a tubercle. 
It is not in touch with any other rib. The rib behind the groove starts at an 
umbilical tubercle and either bifurcates therefrom with another rib, or is the 
only rib continuous with the lateral edge of the tubercle, or emanates from the 
anterior surface of a tubercle, from which another rib starts in continuous 
line with its lateral edge and still another from its posterior side. This rib 
behind the groove cuts off two or three other ribs. As it crosses the external 
surface it becomes thicker and in the last two sulci of the larger specimen 
very much so. There are six of these grooves on the last whorl. The course of 
the other ribs is somewhat irregular. Many of them are very slightly convex 
forwards near the middle of the flank. A few are straight in this region. They 
mostly cross the external surface with scarcely any convexity forwards. In 
some of those near the sulci, however, the forward inflexion on the external 
surface is greater. The spaces between the ribs are much broader than the 
ribs and also broader than the nearest sulcus. On the end of the last whorl, 
which possibly partly represents the posterior end of the body-chamber, the 
interspaces become much broader and the ribs thicker. In the second specimen, 
of which apparently a large part of the body-chamber has been preserved, 
the ribs are very thick on this portion and the interspaces very broad. 
The lobe-line resembles most that of Holcodiscus. The external saddle 
and both lateral saddles are symmetrically divided by a secondary lobe. The 
external saddle is slender and longer than the others. The first lateral lobe 
is trifid and longer than the ventral lobe. The second lateral saddle does not 
touch the umbilical margin. On the umbilical surface the lobe-line runs 
backwards and forms three very small saddles. 
Measurements : 
Small spec. Large spec. 
Diameter 
64 mm. 
(1) 
62 mm. 
(1) 
Height of last whorl 
27 „ 
(0-42) 
26 ,, 
(0*42) 
Thickness of last whorl 
21 ,, 
(°*33) 
22 ,, 
(o-35) 
Height of penult, whorl 
16 ,, 
19 ,, 
(°'3°) 
Thickness of penult, whorl 
13 » 
16 ,, 
(0-26) 
Diameter of umbilicus 
18 ,, 
(0-28) 
18 ,, 
(0-29) 
The end of the last whorl of the type (small specimen) is damaged on one 
side and its thickness cannot therefore be accurately given. 21 mm. is its 
approximate dimension. The sides of the last whorl of the large specimen 
are also damaged and its thickness is therefore also given approximately. 
The measurements of the penultimate whorl of the type are not comparable 
with those of the last whorl, because they had to be taken on another diameter. 
