20 
Annals of the Transvaal Museum 
flanks; in D. simplex they are at the most only very slightly convex forwards 
on the middle of the flanks. In D. phyllimorphum the external portion of the 
mouth-edge forms a broad tongue-shaped anterior process; in D. simplex this 
process is narrow. The external lobe of the lobe-line of D. phyllimorphum is 
much broader than that of our form. Kossmat compares his species with 
D. Larteti Seunes (12, p. 175), a species placed by de Grossouvre in his 
genus Schluteria (10, p. 218, PI. XXXIV, figs. 2, 3). The differences’ between 
D. Larteti and D. simplex are so striking that it is not necessary to enumerate 
them here; however, the old mouth-edges form a similar anterior process on 
the external surface; in D. simplex it is perhaps slightly more pointed. A com- 
parison with D. diphylloides Forbes sp. is more difficult. I could not lay my 
hands on Forbes’ original description. Stoliczka calls D. diphylloides com- 
pressed ( 4 , p. 119), and Kossmat, who has studied the type, describes its flanks 
as flattened (12, p. 174). Pervinquiere, in describing ammonites from Tunis, 
refers some to Forbes’ species as Puzosia {Latidor sella) diphylloides Forbes, 
and states of an adult specimen, that its flanks are nearly flat ( 18 , p. 141). 
Even if the Odium specimens figured by Stoliczka are left out of discussion, 
we must come to the conclusion that the flanks of D. diphylloides are slightly 
convex, judged from the Pondicherry specimen figured in fig. 8 of PI. LIX of 4 . 
Fig. 9 of PI. XIX in Kossmat (12) also shows convex flanks. The figures of 
Pervinquiere’s specimens show clearly, that their flanks are, in accordance 
with the text, nearly flat. I therefore conclude, that the flanks of D. diphylloides 
are slightly convex; in D. simplex the flanks are quite flat. Stoliczka’s figure 
mentioned above does not show old mouth-edges. These are, however, well 
visible in Kossmat’ s figures. They are in the first place convex forwards on 
the middle of the flanks, and secondly they form a broad tongue-shaped 
anterior process on the external surface. In our form they are at the most 
only very slightly convex forwards on the flanks, while the tongue-shaped 
process is not broad but very narrow. In Pervinquiere’s specimens the 
tongue-shaped process is also very narrow. The figures of some of them show 
quite clearly, that the mouth-edges are slightly convex forwards on the middle 
of the flanks. Pervinquiere unites with Puzosia {Latidor sella)*" diphylloides 
Forbes sp. the specimens from Vancouver, described by Whiteaves as 
Ammonites Selwynianus. Desmoceras Selwynianus Whiteaves sp. ( 7 , Pt ii, 
p. 104, PI. XIII, fig. i) differs from D. simplex in the following points: the old 
mouth-edges are more convex forwards on the middle of the flanks and the 
tongue-shaped process on the external surface is longer. The flanks of the whorl 
are decidedly convex as shown in the figures and according to the text, for 
although the sides are said to be somewhat compressed, the whorls are also 
stated to be thickest near the middle of the sides. The Desmoceras -described 
by de Grossouvre as D. pyrenaicum (10, PI. XXXVII, fig. 9), but which 
according to Pervinquiere does not belong to that type ( 18 , p. 142), shows 
great resemblance to D, simplex. The figure seems to show, that the old mouth- 
edges are fairly straight on the flanks, but form a very broad, tongue-shaped 
anterior process on the external surface. The sides seem to be flattened and 
convergent towards the centre. 
Four specimens of this species have been found, three of which have been 
used for the description. 
Desmoceras crassum n.sp. PI. IV, figs. 3, 4, text-fig. ii. 
Shell thin, discoidal, umbilicated. Whorls higher than broad. Greatest 
thickness of the whorl in the middle of the flanks. Sides of whorl slightly 
convex. External surface very broad and strongly convex. External surface 
