338 The American Geologist. •^"''*' ^^^^ 
genus Baena has now been traced tjack through the Wa- 
satch, the Puerco, and the Laramine, to the Judith River and 
Belly River beds of the middle of the Upper Cretaceous ; and 
we may confidently expect to find in some freshwater de- 
posits of the Lower Cretaceous other forms connecting the 
germs with Probaena. It is interesting to note the fact that, 
while the Amphichelydia died out in Europe during the 
Lower Cretaceous, they persisted in North America until 
the Uinta. Furthermore, that it held its ground long after 
•one of the great superfamilies to which it had given origin, 
the Pleurodira, had been driven from the continent; for we 
know of no members of the latter group in our country 
after the Cretaceous. 
Taking up next the Trionychoidea, the soft-shells, we 
.must believe that those of the family Trionychidse had 
descended from forms which lived in North America during 
the Upper Cretaceous. Several species occur abundantly 
in the Laramine and in the Judith River and Belly River 
beds of Montana and British America. Of these Cretaceous 
species, all that are sufficiently well known belong to the 
■genus Aspideretes, those with the preneural, and the writer 
believes that this is the most primitive known genus of the 
family. So far as we know, no important changes have 
taken place in the structure of these animals since the mid- 
dle of the Upper Cretaceous. Aspideretes beecheri is based 
on a specimen at Yale from the Laramie of Converse coun- 
ty, Wyoming. Nearly the whole of the skeleton, except the 
head is present. It differs little from others of the family 
living to-day. Apparently this species comes to us from 
the still older Judith River beds. We cannot, therefore, 
doubt that the family had had a long previous history; and 
it is to be expected that more primitive trionychids will 
yet be found in some of the freshwater deposits of the 
Lower Cretaceous, in company with remains of the early 
representatives of Baena. Ameghino has reported Creta- 
ceous trionychids from South America. The living Trio- 
nychidse appear to love flowing waters; and the same habit 
appears to have possessed the other known forms. We 
may therefore expect to find their remains only in river 
deposits of the Lower Cretaceous. 
