PSEUDOTISSOTIID_E, TISSOTITDA. 41 
PLESIOTISSOTIA Peron. 
This genus has been founded by Peron entirely upon the differences of 
the sutures as compared with Hemitissotia. The first lateral saddles are 
broad and very deeply divided by a median marginal lobe and each arm 
is phyllitorm and is also subdivided by a median marginal lobe; the 
remaining saddles are phylliform and equally subdivided by median 
marginal lobes. It is a question whether these peculiar sutures really 
represent another group or are simply retrogressive modifications in the 
genetic line of Hemitissotia. ‘The compressed and costated form does not 
indicate affinities, but, as stated by Peron, the divided saddles are similar 
to those of Hemitissotia precipua, except the first laterals, which are narrow 
and irregular in outline in the latter. 
PLESIOTISSOTIA MICHALETI Peron. 
Plesiotissotia michaleti Peron, 1897, Mém. Soc. géol. France, Paléontologie, Vol. 
WIUL NOs JING fol Wa, mes, M5 tS 
A highly compressed keeled form with costze having tubercles on the 
umbilical shoulders, as in some species of Hemitissotia. The sutures are 
described in the notice of the genus. 
Locality: North Africa. 
Age: Senonian. 
TISSOTIIDA Hyatt. 
This family name is here much narrowed in its application as compared 
with what it was in my chapter on Cephalopoda in Zittel’s Text-book. It 
is now considered applicable to a series of genera that includes only Tissotia 
and its immediate allies, excluding Pulchellia, Psilotissotia and Lopholobites. 
The genera can be described as having keeled forms, with channels only in 
primitive genera. The keels have a crenulated or nodose stage in a number 
of primitive genera, but are continuous in the flattened forms. Coste are 
present in the globose primitive forms and are usually tuberculated, and 
when they disappear the nodes are apt to persist. The venters lose their 
keels and become rounded or flattened in old age. One genus has a hollow 
keel (Paratissotia) and others may have hollow keels. So far, however, the 
only fact in favor of this is the presence of prominent keels on the shells 
that have no corresponding keel elevations on the casts. The sutures are 
