PULCHELLUID. 137 
continuous at any stage and can not even be accurately described as ridges. 
The term carina or keel should be confined entirely to the continuous 
azygous ventral elevation. The term bicarinate is confusing and might be 
especially troublesome if-ocvasion should arise to describe a form having 
a really double or split keel. A further modification of the development 
takes place when a keel arises upon the smooth rounded venter of the 
earlier stages as in Psilotissotia. This form is apparently transitional to 
true Tissotidee, but these affinities disappear upon comparing the ontogeny 
with that of Tissotiidee, and especially when the relations of these to the 
flat ventered and keeled and chamneled forms of Pseudotissotia are recog- 
nized. The sutures of Psilotissotia are also decidedly Pulchellian and there 
are also transitional forms connecting it with Psilopulchellia. Lopholobites, 
so far as known, appears to be adequately accounted for as a retrogressive 
modification of Psilotissotia or some of the smooth forms with which it 
agrees in external characters. This suggestion requires, of course, to be 
tested by the comparative study of its development and that of the similar 
forms of this family.* The natural arrangement of these genera upon the 
basis of their ontogeny seems therefore to be as follows: 
Pulchellia 
| 
Nicklesia Subpulchellia Psilotissotia 
| 
paieelen align ate Penner es 
| 
Heinzia 
! 
It seems obvious from the development of the young of most genera 
and the apparently full-grown Subpulchellia, and from the evidence of the 
sutures, that this group is closely related to Engonoceratidz. If this be so, 
the latter can be explained as a retrogressive form evolved from Subpulchel- 
lia as its most probable Neocomian ancestor. The supposed relations of 
some of the genera to Stoliczkaia are discussed under the head of Pulchellia. 
The parallelism between some of these forms of Pulchellia and the Hoplitidee 
is so close that it requires the evidence of their younger stages for their 
separation. It is closer than between this genus and any one of the Heinz- 
iidze, because of the presence of the line of double elongated tubercles in 
the latter. 
«The Pulehelliidze were not mentioned in my Cephalopod chapter in Zittel’s Text-book, owing to 
the accidental omission in copying of a page of the manuscript. 
