Bennettites dacotensis Macbridk. — Calvin. 79 
is considerably narrower than in allied forms and that the 
terminal segment shows a widening and no trace of spiniform 
process. There are also several other minor points of differ- 
ence. 
But except its outward form or outline the above described 
fossil tells us nothing about the details beyond what was 
known before, unless the indistinct outline of a metastomatic 
plate may be so regarded. This is a quadrilateral rhombic 
area, a little in front of the central part of the body, margined 
by four furrows and corresponding to a similar area visible in 
some specimens of Eurypterus which show the ventral aspect. 
ON THE GEOLOGICAL POSITION OF BENNETTITES 
DACOTENSIS M ACBRI DE, WITH REMARKS ON 
THE STRATIGRAPHY OFTHE REGION 
IN WHICH THE SPECIES WAS 
DISCOVERED. 
By SamdeTj Calvin, Iowa City, Iowa 
Since professor Macbride's paper on Bennettites dacotensis 
was published in the American Geologist for October, L893. 
there have been numerous inquiries respecting the exact geo- 
logical horizon from which the cycads were derived. The 
close resemblance and the intimate relationship indicated be- 
tween the Dakota fossil and '/'//sonic marylandica Fontaine. 
while not conclusive, would yet point toward a common hori- 
zon for the two species, and so make it possible to correlate 
the Potomac -formation with a definite Mesozoic horizon in 
the Northwest. Professor Macbride's paper left the strati- 
graphical position of his species undecided. To settle the 
question definitely, if possible, the writer recently made a 
visit to the locality that furnished the types of Macbride's 
species. 
Specimens of Bennettites are not very numerous in the 
Black Hills of South Dakota. At all events not very many 
have yet been brought to light. All the individuals at present 
known have been found in a rather limited area around Min- 
nekahta. a small stat ion on the Deadwood branch of the B. 
& M. railway. By far the greater number, some Forty or 
fifty altogether, were discovered on an area of only a feu 
