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 Pusispira 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 Glytocysiites 

 sp. undet., Helopora mucronata, Arthrodema armatum, Nematopora ovalis, N. granosa, 

 Pachydictya pumila, Rhinidictya minima, Homoirypa similis, Mesotrypa discoidea, Orihis 

 meedsi var. germana, Clitambonites diversus, Schmidtella subcequalis, 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 Pusispira 

 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 schucherti 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, (pi. 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: 

 Lingnla iowensis, I* hurlbuii, L. n. sp., Schizotreta pelopea, Strophomena trilobata, 



' It la 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 nacouracles, tnough we would doubtless have fallen Into others and 

 In the end perhaps have prod uced more confusion than prevails now with the provisional nomenclature whloli 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 1802 that they were fully understood and characterized 

 so as to be recognized at once by their fossils and llthological 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. 



