26 
Annals of the Transvaal Museum 
and the flanks. The sides curve gently into the sloping umbilical surface. 
Height of the umbilical surface moderate. Involution slightly more than one- 
half of the preceding whorl. 
The ornamentation consists chiefly of umbilical tubercles of which there 
are about twelve or thirteen on the last whorl. These tubercles are only present 
on the last whorl and a quarter, the earlier whorls being smooth. The tubercles 
are transversely elongated; highest near the umbilical edge, broadening and 
ultimately disappearing towards the middle of the flanks. The shell surface 
is very much worn and large patches have peeled off. As far as can be made 
out the shell was smooth, except for the tubercles, on flanks and external 
surface. The umbilical surface shows very fine growth-lines or ribs, closely 
but irregularly placed and concave forwards. It is very probable, that these 
fine lines continued on the flanks, but this is not shown in the specimen. A 
smaller specimen, with tubercles on three-quarters of the last whorl only, shows 
that the shell is covered with very fine growth-lines, which are concave for- 
wards on the umbilical surface, convex forwards on the inner half and concave 
forwards on the outer half of the flanks, and very slightly convex forwards on 
the external surface. 
The lobe-line is a typical P achy discus one. The external lobe is just as long 
as the first lateral one. The external saddle, the two lateral saddles and the 
first auxiliary saddle are deeply divided by a secondary lobe. The saddles 
Text-fig. 14. P achy discus simplex. Lobe-line of type up to the umbilical suture 
on a radius of 21 mm. x 3-3. 
diminish gradually in height inwards. Both lateral lobes are trifid. The second 
lateral lobe is shorter than the first. The first auxiliary lobe is also very long. 
The umbilical portion of the lobe-line runs obliquely backwards and consists 
of four auxiliary saddles and lobes. 
Measurements : 
Type 
Paratype 
Paratype 
Diameter ... 
40 
mm. (i-oo) 
17*2 mm. 
(I-OO) 
28 mm. 
(I-oo) 
Height of last whorl 
15 
„ (0*37) 
6-9 „ 
(0-38) 
II 
(0-39) 
Thickness of last whorl . . . 
157 
» (0-39) 
7*5 » 
(0*44) 
12 
(0-43) 
Height of penult, whorl . . . 
8 
„ (0-20) 
4 
(0-23) 
6-4 ,> 
(0-23) 
Thickness of penult, whorl 
8 
„ (0-20) 
4*2 „ 
(0-24) 
6-5 
(0-23) 
Diameter of umbilicus ... 
13-2 
.. (0*33) 
5-4 .. 
(0-31) 
8-6 „ 
(0-31) 
The type and the smallest specimen are quite normal and have not suffered in 
the least from pressure; both are wholly septate. The middle specimen has become 
slightly irregular from pressure. 
