Annals of the Transvaal Museum 
19 
our specimens varies from stretched oval to nearly circular. One specimen 
shows a fine carina. These shells greatly resemble Baculites teres Forbes as 
figured by Stoliczka ( 4 , PL XC, fig. 12), in fact it seems to me practically 
impossible to distinguish between the two if one excepts the sulci of B, teres. 
Genus DESMOCERAS Zittel. 
Desmoceras simplex n.sp. PI. Ill, figs, ii — 16, text-fig. 10. 
Shell thin, discoidal, umbilicated. Whorls higher than broad. Sides of 
whorl fiat. Greatest thickness of whorl on the external portion of the flanks. 
In younger whorls the flanks are practically parallel. External surface broad, 
convex and smooth except for growth-lines and mouth-edges. The last portion 
of the last whorl of the large specimen is more strongly convex than its first 
portion and than the last whorl of the type. There is no line of demarcation 
between the flanks and the external surface. The umbilicus is extremely 
narrow. The flank passes abruptly into the umbilical surface, which is of 
moderate height and vertical to the plane of symmetry. The innermost portion 
of the umbilical surface slopes away from the centre and towards the plane of 
symmetry, and therefore the radius of the umbilical suture is longer than that 
of th6 middle of the umbilical surface. The involution is such, that only an 
extremely narrow strip of the preceding whorl remains uncovered. 
The surface of the shell is smooth, except for some growth-lines, especially 
in the vicinity of the old mouth-edges. Old mouth-edges are visible as very 
shallow grooves on the shell and on the cast. These grooves are well visible on 
the external surface and on the external portion of the flanks, where they are 
bordered behind by a low rib. They disappear, however, towards the middle 
of the flanks. On the cast they are visible till near the umbilical edge. On 
the flanks they are straight or very slightly convex backwards and directed 
somewhat forwards. On the end of the last whorl of the large specimen they 
are very slightly convex forwards on the middle 
of the flanks. They run more forwards on the 
external surface, where they surround a tongue- 
shaped anterior process of the mouth-edge. 
The lobe-line is typical for Desmoceras. All 
the saddles are bifid and all the lobes, except 
the external one, are trifid. The external lobe 
and the first lateral lobe are of equal depth. 
Six saddles are visible up to the edge of the 
umbilicus in the type ; in the paratype there are 
seven saddles on this portion ; these are arranged in a straight line and diminish 
gradually in height from the external saddle inwards. 
Measurements : 
Type 
Paratype 
Paratype 
Diameter ... 
25-7 
mm. (i-oo) 
26-6 mm. 
(I-OO) 
44 mm. 
(I-oo) 
Height of last whorl 
14-3 
,, (0-56) 
14-5 „ 
( 0 - 55 ) 
24-6 ,. 
(0-56) 
Thickness of last whorl . . . 
10-5 
(0-41) 
12 
( 0 - 45 ) 
17 
( 0 ' 39 ) 
Height of penult, whorl . . . 
7-5 
„ (0-29) 
7*6 „ 
(0-29) 
12 
(0-27) 
Thickness of penult, whorl 
6*4 
(0-25) 
7-2 „ 
(0-27) 
9-2 „ 
(0-21) 
Diameter of umbilicus . . . 
2 
„ (o-o8) 
2-2 ,, 
(o-o8) 
3*4 
(0-08) 
It is quite apparent that the systematic position of Desmoceras simplex is 
in the close vicinity of D. diphylloides Forbes sp. and D. phyllimorphum 
Kossmat. It differs from the last through its flat flanks. Further the old 
mouth-edges of D. phyllimorphum are convex forwards on the middle of the 
Text-fig. 10. Desmoceras sim~ 
plex. Lobe-line of type up to 
the umbilical edge on a radius 
of 9 mm. X 3. 
2 — 2 
