138 
Transactions of the Royal Society of South Africa. 
The outer whorl flattens out in all the large examples, but the two quadrate- 
whorled paratypes do not quite agree in ornamentation either with the 
holotype or with each other. No. 1 1367 is transitional to the var. sparsicosta, 
described below, and has a very indistinct median lateral tubercle : in 11368 
this tubercle is as pronounced as in the example figured by Woods. 
35. Mortoniceras stangeri (Baily), var. sparsicosta, nov. 
(Plate V, fig. 1.) 
In some of the examples of M. stangeri, described above, the inner 
whorls are less closely costate than in the type. These are transitional 
to the present variety, which is characterised by the comparatively coarse 
and distant tuberculation of the inner whorls, and the depression until a fairly 
late stage of the whorl-section. Baily 's paratype 11368a, the internal 
suture-line of which was figured on pi. xxiii, fig. 3c, of the writer's Zululand 
paper, also specimen No. C 19444 (text-fig. la, p. 297, loc. cit.), belong to 
this variety. The lateral view of the latter specimen is represented in fig. 1 
of Plate V, and has dimensions : 295 — 27 — 25 — 53. 
Crick included specimen C 19444 in what he listed as an " intermediate 
group between M . stangeri and M. soutoni," but none of the examples in his 
list has any resemblance to M. soutoni. Moreover, there is no description of 
any of these Mortoniceras, and even the most typical example of M. soutoni 
was erroneously listed as M. stangeri. 
36. Mortoniceras stangeri (Baily), var. densicosta, nov. 
(Plate V, fig. 2.) 
This is a more finely costate variety, typically represented by specimen 
C 19456, here figured, of the following dimensions : 125—28 — 25 — 52. The 
inner whorls of this specimen also seem more compressed, though slightly 
crushed. Some transitional examples (C 19450, C 19450a, C 19462) 
connect this variety with the typical M. stangeri, just as this again is 
connected by a series of gradations with the var. sjjarsicosta. The outer 
whorls of the three forms here described are very similar, and tend to 
weaken the tuberculation of the costae. 
The occurrence of distantly and closely ribbed varieties is of interest in 
connection with a recent paper by Professor Salfeld.* In the varieties of 
M . stangeri, however, there is no correlated change in whorl-section, and 
the var. densicosta is not so common as the other forms, being typically 
* " Bemerkungen zu v. Bubnoff, etc," Zeitschr. f. indukt. Abstamm. und Vererb. 
Lehre, 1921. 
