88 PSEUDOCERATITES OF THE CRETACEOUS. 
COILOPOCERATIDA Hyatt. 
This includes genera having the primitive first lateral saddles far more 
variable in development than in Sphenodiscidee. Aconeceras has only one 
long deeply divided first lateral. Platylenticeras and Coilopoceras have 
three according to the method of reckoning adopted below, but the 
elements are the same as in Aconeceras. Aconeceras, Styracoceras, and 
Platylenticeras probably have solid keels, although there are no observations 
on this point that can be quoted. 
The development and adult form of Styracoceras indicate that the 
more primitive forms of this family had truncated venters with keels and 
lateral tubercles, and were similar in external aspect to Buchiceras. 
’ Coilopoceras has a hollow keel. The sutures and development at first 
seem to place it in the same group with Sphenodiscus, but the two principal 
lateral saddles, the median lateral lobe (second lateral lobe) with long 
tongue-shaped marginal saddles, and the aspect of the auxiliaries in the 
young indicate association in the same family with Aconeceras. 
These remarks show that while these genera are sufficiently distinct, 
their association in a group together is made more to call attention to 
certain suggestive similarities than with any idea that they really belong 
together exactly as described below. 
The evidence that this family was directly derived from Phylloceras or 
some similar form rests upon the general outlines of the saddles, which are 
phylliform, especially in the neighborhood of the umbilici, and the widely 
spreading and peculiar lobes. The dorsal sutures are as usual less changed 
than the external inflections and these have almost exclusively phylliform 
outlines like those of Phylloceratida. The antisiphonal has a long narrow 
form with a bifid end and although it is serrated or slightly branching and 
not so simple as in Phylloceras, it has a similar form. 
As mentioned in the generic description of Aconeceras the sutures of 
A. nisum make a nearer approach to those of Phylloceras than any other 
genera of this group or any others except the Sphenodiscidee.” 
PLATYLENTICERAS Hyatt. 
This genus was mentioned in Zittel’s Text-book, page 590, by the author 
and the type given was the same species cited below. The sutures are 
«The manuscript of this last paragraph bears an interrogation mark on the margin.—T. W. 8. 
