40 Transactions of the Royal Society of South Africa. 
the upper converging parts of the sides are provided with two hollows with 
a median crest which is retuse or even emarginate, whilst the lower parts of 
the sides are variously crenated. YIII is perhaps the specimen which 
approximates most closely in these respects, whilst X is cha.racterised by 
sides which are more markedly subparallel than is usually the case, hand in 
hand with w^hicli appears to go the development of the tumour nearer the 
middle of the semicell, as seen in side-view. IX approximates somewhat 
towards var. gregorii in the bigranulate character of the crenations. 
Somewhat more divergent forms are shown in Fig, 15, YII and XI ; these 
are characterised by a rather pronounced delimitation of the apex of the 
semicell as a kind of square- edged apical protuberance, due to the upper 
hollow being deeper than usual — a feature which is also indicated in IX. 
VII is further distinguished by the absence of crenations on the lower parts 
of the lateral margins ; its dimensions were : long., 25-28 /x ; lat., 22 fx ; lat. 
isthm., 6/x; side- and end-views, as in YI. XI is characterised by a 
tendency towards equalisation of the crenations on the lower and upper 
parts of the sides (c/. especially the right-hand side of the semicell), 
although the upper ones are still larger than the lower ones. 
These two specimens lead over on the one hand to that shown in Fig. 15, 
YI, on the other hand to those depicted in Fig. 15, I-Y. The specimen YI 
resembles YII, except that the apex is not so sharply delimited. The 
median crest on the upper part of the lateral margins is still well marked 
though not always retuse, but the crenations on the lower parts of the sides 
are feeble. The dimensions were: long., 28-30 />t; lat., 24 /x ; lat. isthm., 
6 fi; crass., 14-15 /x. Specimens of this kind were also seen with minute 
granules or teeth on the lateral crenations, similar to those in Fig. 15, IX. 
The forms YI, YII, and XI difPer from those in Fig. 15, YIII-X, in that 
they tend to show a gradual convergence of the lateral margins, beginning a 
little way above the base of the semicell. This feature is clearly indicated 
in IX. 
The remaining forms (Fig. 15, I-Y) show this convergence to a more 
marked extent, and this is accompanied by an increasing equalisation of the 
crenations on the lateral margins (cf. var. simplicius, Schmidle, Hedwigia, 
xxxiv, 1895, p. 77, Tab. I, fig. 10). Specimen III is most like 0. stihpro- 
tumidum, but has two crests instead of one on the upper parts of the lateral 
margins ; in lY and Y, whilst the upper crenations are still the larger, they 
are rounded like the lower ones and not retuse ; in II the distinction 
between the lower and upper crenations is but feebly indicated, whilst the 
extreme condition is reached in specimen I, with a very regular convergence 
of the lateral margins and practically uniform crenation. 
These individuals, with converging lateral margins and a tendency 
towards uniform crenation, are the largest of the series, although connected 
with the smaller ones by specimen YI. Their dimensions are : long., 
