IOWA ACADEMY OP SCIENCES. 
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teeth evidently related to Dipterus, but so different as probably 
to make generic separation necessary. 
But more interesting than all the rest, and far outnumbering 
the teeth that could at first sight be referred to Dipterus or to 
related genera, is a vast assemblage of teeth of varying shapes 
and dimeusious, that bear a striking external resemblance to 
the crushing teeth of certain genera of sharks. In the opinion 
of Dr. C. R. Eastman, however, it is doubtful if there are any 
Selachian teeth in the entire lot. He finds that, microscopi- 
cally, they all, so far as sections have been made, are identical 
in structure with the teeth of Lung fishes, or Dipnoans. They 
seem, indeed, to be primitive Dipnoans exhibiting a stage of 
evolution not far removed from the point whence the Dipnoan 
and Elasmobranch types diverged; and their careful study will 
doubtless throw much light on the nature of the relationships 
existing between these two groups of fishes. Dipterine fishes 
have long been known from the Devonian of eastern Europe, 
but it is only recently that this type has been found in the 
Devonian of America. Until the discovery of the State quarry 
fish bed, our Devonian Dipterines all belonged to a single genus 
and came from the upper Devonian formations of Pennsylvania. 
Now we find the type in the Mississippi valley, and here it is 
represented by several genera, and is connected by intergrada- 
tions with exceedingly primitive Dipnoan forms. The material 
has been placed in the hands of Dr. Eastman, whose full report 
on the subject will be awaited with much interest. 
Distribution . — At present the state quarry limestone is 
known only in Johnson county, Iowa, though it doubtless 
occurs at other points in Iowa and adjacent states. The main 
body occurs in sections 5 and 8 of Penn township (T. 80 N. , R. 
6 W.). It is found in the bluffs on the west side of the Iowa 
river from the north line of section 5 to a little more than one- 
fourth of a mile below the north line of section 8, the principal 
development occurring near the south side of the first named 
section. The width of the area occupied by the formation in 
this region is less than half a mile. In fact in following up the 
small tributary valleys the state quarry stone is in most cases 
found to disappear in less than one- fourth of a mile. 
A second body of state quarry limestone is found near the 
southwest corner of section 20, of Graham township, at which 
point the formation is almost exclusively crinoidal as to com- 
position; a third body of this limestone, but of no great thickness. 
