27.2 STUART WELLER 
with this form at Rockford is Prodromites gorbyi which occurs also in 
the Chouteau limestone of central Missouri. This latter goniatite is 
the most advanced one of the Mississippian faunas, having, as it does, 
a secondarily lobed suture such as, at no very distant period in the past, 
was considered to be characteristically Mesozoic in type. Another 
peculiar cephalopod in the fauna is Tvibloceras digonum which occurs 
in the fauna at various localities. A peculiar type of pelecypod is 
found in the genus Promacrus, which occurs also in the early Mississip- 
pian beds of Belgium. These and many other forms in the fauna char- 
acterize it as something distinctly younger than any Devonian fauna, 
with numerous bonds of affinity uniting it with the higher and more 
typical Mississippian faunas. However, there occur associated with 
these characteristic portions of the fauna certain species, especially 
among the pelecypods, which are clearly Devonian derivatives, and, 
strange to say, their relationships are usually with members of the 
Hamilton fauna, rather than with the higher Devonian faunas of the 
Eastern Continental Province. The Hamilton relationships of the 
fauna are perhaps best seen in the fauna of the Glen Park limestone,* 
where the pelecypods and gastropods are all close allies of Hamilton 
forms, and where one form even seems to be specifically identical, but 
associated with these is a member of the highly characteristic Missis- 
sipian genus Syringothyris.? 
The origin of this southern Kinderhook or ieneuean fauna is 
believed to have been in the Atlantic Basin, where Middle Devonian 
faunas of Hamilton type had probably retreated as the Upper Devo- 
nian immigrants became established in the Eastern Continental Prov- 
ince, or where they had persisted during Upper Devonian time, having 
never been encroached upon by the immigrants. During the long 
lapse of time most of the species had been modified, and there had 
been absorbed into the fauna a new element from some unknown 
region. The return of this fauna into the Mississippi Valley Basin 
marks the opening of the Kinderhook epoch and the Mississippian 
period. 
t Weller, Trans. St. Louis Acad. Sci., XVI, 435-71. 
2 The species described in the Fauna of the Glen Park Limestone (loc. cit). as 
Spirifer jeffersonensis, has since been definitely identified as a member of the genus 
Syringothyris. 
