MOJSISOVICSITD 4. 25 
subphylliform marginal saddles and excessively short pointed marginal 
lobes that are hardly more than serrations. The ventral lobe is very broad 
and divided. The first and second lateral lobes are narrow and similar to 
those of Buchiceras, but it should be noted that the dorsal sutures are 
unknown, and these may be quite distinct. The third lateral lobe is entire, 
and the fourth saddle hardly past the entire stage, exhibiting only a slightly 
trifid outline. Such sutures exhibit affinities with the smooth primitive 
ancestral stock of the Psiloceratidee of the Jura and other forms of Pachy- 
campyli descended from these because of their massive broad saddles, so 
entirely different from the narrow, excessively branched saddles of the 
Phyllocampyli and Leptocampyli. I do not, of course, mean that Mojsiso- 
vicsia is probably descended directly from Psiloceras, but it may be a Cre- 
taceous member of a primitive stock which began with Psiloceras in the 
Jura. The intermediate forms are as yet unknown or have not been pub- 
lished. The existence of such a trunk or main branch of a primitive stock 
from which all of the more complex groups are lateral offshoots has been 
inferred from the ontogeny as the most probable way to account for the 
ontogeny of the primitive species of these groups. Thus in the present 
instance the smooth discoidal young of Buchiceras and other genera can be 
readily accounted for if the comparison between them and the later stages 
of Mojsisovicsia is admitted. If such a stock of primitive forms existed, it 
is also easy to account for the maintenance of such primitive smooth psilo- 
ceran-like shells in the later nepionic and sometimes in the neanic stages of 
Cretaceous forms. Otherwise the continued renewal of these in the ontog- 
eny at such late stages must be referred to more ancient ancestors than any 
represented in the Jura. 
MossIsovicsta DURFELDI Steinmann. 
Pai hess l=3: 
Mojsisovicsia durfeldi Steinmann, Neues Jahrbuch fiir Min., Geol., und Pal., 1881, 
1], p. 148, pl. 6. 
The peculiar fossil deseribed under this name has a compressed discoidal 
shell with slight constrictions, open umbilici, and smooth surface that in 
external aspect resembles Traneceras and also some of the discoidal Desmo- 
ceratidee like Pseudophyllites Kossmat, but has entirely different sutures. 
These have an aspect similar to those of Buchiceras bilobatum, but the form 
of the volution differs so widely that no further comparisons can be made 
