THE 
AMERICAN GEOLOGIST 
Vol. V. APRIL, 1890. No. 4. 
CERTAIN FORMS OF STRAPAROLLUS FROM SOUTH- 
EASTERN IOWA. 
By Charles R. Keyes. 
In the consideration of the generic characters of Straparol- 
lus certain forms from the lower Carboniferous rocks of 
southeastern Iowa present some interesting phases which illus- 
trate fully peculiarities formerly regarded of great importance 
in the separation of this genus from Euomphalus. The two 
terms are of common occurrence in the literature of American 
Palaeontology, and have been applied indifferently both to 
planorbiform gasteropod shells having angulated whorls and 
those possessing rounded volutions. The latter features were 
originally regarded as distinctive. Yet the multiplicity of 
forms manifestly belonging to the group founded by Montfort 
has given rise to the establishment of a number of genera 
which can now be considered only as of little or no utility 
and seem best disposed of when placed in the synonymy of 
this genus. Aside from the two leading sections, however, 
these various terms require no further reference here. 
The species from the immediate vicinity of Burlington that 
have been referred to the two groups in question elucidate 
somewhat the true relations existing between Straparollus and 
Euomphalus, both as regards the structure of the shells and 
the probable optimum station of the animals when living. 
