Annals of the Transvaal Museum 25 
the first lateral one. The external saddle, the two lateral saddles and the first 
auxihary saddle are symmetrically divided by a secondary lobe. The saddles 
diminish gradually in height inwards. The first lateral lobe is trifid. The second 
Text-fig. 13. P achy discus antecursor. Lobe-line of type up to the umbilical 
suture on a radius of 25 mm. x 2-5. 
lateral lobe and the first auxiliary lobe do not pass so far backwards as the 
first lateral lobe. The umbilical portion of the lobe-line runs obliquely back- 
wards and consists of four auxiliary saddles and five lobes. 
Measurements : 
Diameter 
78 mm. ; was probably 79 mm. 
(i-oo) 
Height of last whorl ... 
probably 27-4 ,, 
(0-35) 
Thickness of last whorl 
27-4 .. 
(0-35) 
Height of penultimate whorl . . . 
17 
(0-22) 
Thickness of penultimate whorl 
15-7 
(0-20) 
Diameter of umbilicus ... 
28-3 „ 
(0-36) 
Pachydiscus antecursor differs from P. Vaju Stol. sp. in having a larger 
umbihcus and a different sculpturing. P. anapadensis Kossm. is a relatively 
thicker shell. There is great resemblance with P. Jimboi Kossm. In P. Jimhoi, 
however, the thickness of the older whorls is apparently slightly greater than 
the height, whereas in P. antecursor this is the reverse. In P. Jimboi the ribs 
form an angle on the external surface, while in our form they are only slightly 
convex forwards. P. Yokoyamai Jimbo differs from our form in having broader 
whorls. In P. Egertonianus Forbes sp. the section of the whorls is higher than 
broad. There are also umbilical tubercles; in our form there are no tubercles, 
not even in the earliest stages ; ribs are present in our form on whorls of about 
I cm. diameter; the surface of the whorls with a lesser diameter is damaged. 
In certain stages of P. Egertonianus the ribs are weaker on the flanks than 
elsewhere; nothing of this kind is noticed in P. antecursor. The lobe-line of 
P. Tweenianus Stol. sp. resembles that of our form very much; however, the 
shape of the ribs is different in the African form and especially the shape of 
their convexity towards the front on the external surface. The whorls of 
P. Levyi de Gross, are broader than high and their ribs have a different shape 
from those of our form. 
Of this species only one specimen has been found. 
Pachydiscus simplex n.sp. PI. V, figs. 3, 4, text-fig. 14. 
Shell discoidal. Whorls increasing slowly in size. Whorls slightly thicker 
than high. Greatest thickness near the umbilical edge. Sides of whorl and 
external surface convex ; there is no demarcation between the external surface 
