A CIRCUM-INSULAR PALZOZOIC FAUNA. O13 
whether the two forms should be separated at all. Oftentimes 
individual specimens from the Chouteau beds cannot be distin- 
guished from individual specimens from the New York Hamilton 
beds, except in color, the form being essentially the same. The 
presence of this form in the Iowa Devonian beds may be attrib- 
~ uted to the nearness of that area to the border line between the 
two provinces during the period of submergence of the land 
barrier. 
Orthis (Schizophoria) resupinata, Martin. American specimens 
of this species have been described as O. swadlovi, Hall,* but it is 
impossible to separate the American specimens from European 
examples. The ancestor of this species is most certainly to be 
found in O. striatula, Schl. of the European Middle Devonian. 
In the beds of the Chouteau group many intermediate forms 
between the two species are found. The facts of the distribu- 
tion of O. striatula are most interesting. It occurs in the West- 
ern American Devonian faunas under the name O. zowensis, 
Hall. In the eastern portion of America it appears first in the 
Tully Limestone under the name of O. talensis, Vanuxem. This 
represents its first eastward migration. Later, when the land 
barrier was more fully removed, it again migrated to the east, 
and is found in the Chemung faunas under the name O. zmpressa, 
Fall 
Productella hallana,Walcott (= P. disstmalis, Hall). This pecu- 
liar little species occurs abundantly in the Devonian fauna of the 
west and in Europe, and is also present in the very lowest beds 
of the Chouteau group near Springfield, Mo. Itis also present 
in the very lowest beds of the Chemung group in New York. 
Productella pyxidata, Hall. This species is closely related to 
P. subaculeata, Murch., of the European Devonian, and _ its 
ancestry may apparently be traced to that species. 
Rynchonella (Pugnax) acuminata, Martin. This type of Ryn- 
chonella is wholly unknown in the east American province until 
after the period of immigration from the west, when it occurs 
with Preductella hallana, in the very lowest beds of the Chemung 
* Geol. Surv. Iowa, Vol. I., Pt. II., p. 579, Pl. XII., Figs. 5 a—b (1858). 
