C THE PALEONTOLOGY OF MINNESOTA. 
and is now called Cyclospira bisulcata. This leaves the genus Camarella without any known 
representative in the Silurian rocks of Minnesota. 
This lower division of the Fusispira bed is referred to occasionally in the description 
of the fossils as the ‘‘Nematopora bed” or as the ‘‘top” or ‘‘upper portion of the 
Galena shales,” but in most cases the fossils are credited simply to the Galena shales.* 
Fossils are abundant, some of them extremely so. Common forms are plates of Gilytocystites 
sp. undet., Helopora mucronata, Arthroclema armatum, Nematopora ovalis, N. granosa, 
Pachydictya pumila, Rhinidictya minima, Homotrypa similis, Mesotrypa discoidea, Orthis 
meedsi var. germana, Clitambonites diversus, Schmidtella subwqualis, Halliella labiosa and 
Tetradella lunatifera. If a distinct name is desired for this horizon, that of Nematopora 
bed would be appropriate since this genus is represented here by four species and is 
unknown in all the other beds. 
Above the Nematopora horizon we have a series of strata for which the name Fusispira 
bed is proposed and to which the name should eventually be restricted. As has been 
stated already the lower portion of the bed has been separated by Dr. Sardeson as the 
‘‘Camarella bed” while the upper portion he named ‘‘ Lingulasma bed.” ‘The first of Dr 
Sardeson’s names we have shown to be untenable, the second is objectionable because it is 
based upon a fossil that is very rare and in the opinion of the writers probably not 
distinct from the Lingulasma schucherli which is a rather widely distributed fossil of the 
Cincinnati period. We doubt also our right to extend the application of the name to 
strata which Dr. Sardeson holds to be distinct. Our name is based upon the occurrence 
here of at least nine species of Fusispira, four of which seem to be restricted to the bed, 
while two occur also in the Clitambonites bed and the others continue into the lower part 
of the Maclurea bed. 
In Fillmore county, as may be seen from section 4, (pl. xxxv), the Fusispira bed consists 
of a continuous series of thin bedded and more or less pure limestones little short of 100 
feet in thickness. Nearly every foot of the bed as exposed in Prosser’s ravine near 
Wykoff is fossiliferous, and some of the layers are crowded with shells. In tracing the 
bed through Olmsted and Dodge into Goodhue county the lower part becomes gradually 
more and more argillaceous (see sections 3 and 7), the fossils at the same time becoming 
less abundant and finally exceedingly rare or wanting entirely. 
The Mantorville quarry layers, which we place in the lower part of the bed, are 
peculiar in reassuming the magnesian character which had been lost before the bed 
entered Minnesota. The rock here is a firm and durable limestone in courses varying 
from three to thirty-six inches in thickness. All the fossils except the inarticulate 
brachiopods and graptolites occur as casts. We collected here the following species: 
Lingula iowensis, L. hurlbuti, L. n. sp., Schizotreta pelopea, Strophomena trilobata, 
* It is unfortunate that the subdivision of the Lower Silurian strata Minnesota could not be carried out before this 
volume went to press. It would have prevented some naccuracies, taough we would doubtless have fallen into others and 
in the end perhaps have produced more confusion than prevails now with the provisional nomenclature which was adopted 
by agreement among the several authors who have contributed to the work. Although we had a working conception of the 
various subdivisions, it was not till the close of the field season of 1892 that they were fully ufiderstood and characterized 
so as to be recognized at once by their fossils and lithological peculiarities. By this time, however, nearly 400 pages of the 
volume had been printed, and it is in this portion that most of the errors and ambiguities occur. 
