PSEUDOTISSOTIID.®. 35 
The relations of the genera in this family can only be estimated by 
their full-grown shells and sutures, and doubtless any arrangement that 
can now be made will be only provisional. So far as the facts 20, 
Pseudotissotia is a flat-ventered, keeled, and channeled form until a late age, 
losing its keel in old age and having so close a resemblance to Tissotia 
tissoti that it seems to be the only form having any claims to be considered 
the ancestor of that species, as first pointed out by Peron. 
Choffaticeras, wntil a late age, has a venter with keel and channels like 
those of Pseudotissotia in C. meslei but combined with an inflated volution 
and deep, abrupt umbilici and highly inclined, convergent sides. In other 
species the line of modifications indicated by the later stages of its ontogeny 
leads into forms having subacute venters at a comparatively early age, and 
possibly the keeled and channeled stage with its flat venter may have 
altogether disappeared in some of these. The highly involute, compressed- 
keeled forms of Hemitissotia follow these in the same line of modification 
and as their sutures also coincide and they occur in the Senonian, whereas 
all of the above-described genera are Turonian, Peron’s idea that they are 
the direct descendants of Pseudotissotia seems to be well sustained. 
That these are not transitional to true Tissotia becomes apparent when 
it is recognized that the type form of that genus has an ontogenetic history 
like that of Psewdotissotia and is probably, as stated in the deseription of 
the Tissotiidze, the most primitive member of a series of forms distinguished 
by their differences of development as well as by their simpler and more 
retrogressive sutures. 
Although the sutures differ decidedly, the forms of more primitive 
species like Pseudotissotia galliennet and their keels appear to place them 
provisionally nearer to the Buchiceratidee than to the keelless forms. I have 
had no fossils for examination in this family, but the literature and the 
figures given by Grossouvre and Peron have been sufficient to enable me 
to arrange the forms provisionally and to make comments upon their 
probable relations that will, it is hoped, attract attention and lead those 
who have better opportunities to test the truth of the views presented 
below. 
PSEUDOTISSOTIA Peron. 
Peron’s typical species, Ps. galliennei, is a discoidal form with keel and 
channels, having obviously, as observed by Peron, genetic affinities with 
