46 PSEUDOCERATITES OF THE CRETACEOUS. 
the stage represented by the next figure, the forks of the dichotomous costz 
are becoming obsolete and being resolved into short coste, so that there are 
two short nodose coste between the larger ones. This is obviously, how- 
ever, very irregular, since in the figured specimen, which has a diameter of 
85 mm., there is still one dichotomous costation. It is obvious, too, that the 
costee, bemg very heavy, become fold-like with age. The longer cost 
have nodes on the outer ends along the ventro-lateral angles, and nodes 
along the umbilical shoulders, which persist throughout the ephebic stage 
and are present as very broad, low folds in the gerontic stage. According 
to Peron’s description and figures, the short costae disappear and are appar- 
ent only as simple nodes in large specimens. 
This is a compressed form of this genus having an entire keel at an 
early stage, and a close ally of the European species M. nodosa. Peron 
has clearly shown that Bayle confounded two species under this name, but 
I doubt whether Bayle’s Tissotia fowrneli, figs. 4-5 of pl. 40, is identical 
with ewaldi. 
Locality: North Africa. 
Age: Base of Senonian. 
MeratissoTia RopINI (Thiolliére). 
Ammonites robini Thiolliére, 1848, Ann. Soc. d’Agriculture de Lyon, Vol. XI, 
jolt al 
Buchiceras ewaldi Fallot, 1885, Ann. sci. géol., Vol. XVIII, pl. 3, figs. 1, 2.7 
Ammonites cfr. ewaldi Redtenbacher, 1873, Abhandl. K.-k. geol. Reichsanstalt, 
Vol. V, pl. 22, figs. 5 a-i. 
Tissotia robini Grossouvre, 1893, Ammonites Craie supérieure, pl. 4, fig. 1 (not 
fig. 2 b). 
Tissotia ewaldi (pars) Grossouyre, ibid., pl. 9, fig. 5. 
This shell has a compressed form, and the adult figured by Grossouvre 
at a diameter of about 50 mm. has a truncated venter with prominent elon- 
gated tubercles on the ventro-lateral angles and a prominent continuous 
keel. At the end of this volution, or say at a diameter of 55 mm., accord- 
ing to Grossouvre’s figures, these tubercles begin to disappear, and at a 
diameter of 80 mm. they are absent, and the venter has consequently lost 
its truncated aspect and become subacute. This agrees also. with Redten- 
bacher’s figure of a specimen which is 83 mm. in diameter, and in which 
