NIAGARAN CEPHALOPODS 
293 
occupying the large siphuncle of the Niagaran eephalopod played 
a farf more important function in the life of the animal than 
does the slender remnant in the nautilus, the real function of 
whose siphon is not known with certainty. 
Fragments of these large siphuncles constitute the chief part 
of the record left by the straight nautiloids which thrived in 
the Niagaran seas of east-central Iowa. In rare cases a part of 
the shell and a few of the septa have been preserved with the 
siphuncle ; more commonly it is a cast of the shell that is found. 
Silch specimens show the relation of the siphuncle to the shell 
and septa but several of the species are known only from a few 
segments of the siphuncle alone. The occurrence of such re- 
mains in Iowa has been noted by Calvin^ in the Dubuque and 
in the Delaware county reports and also by Savage^ in the Jack- 
son county report. Some of the specimens described in this 
article were doubtless collected during the prosecution of the 
field work in the counties named. 
A paleogeographic map^ of North America during the Nia- 
garan epoch shows that the rocks of this age in Iowa are but 
a part of a series of disconnected outcrops extending east into 
Illinois then north along the west shore of Lake Michigan then 
east again in the upper peninsula of Michigan and across the 
north end of Lake Huron into Ontario and on into New York. 
The Niagaran outcrops just pointed out have yielded several 
species of these interesting cephalopods and they have been 
known to scientists for nearly a century. As early as 1823, 
Dr. John J. Bigsbyifead before the Geological Society of London 
a paper entitled ‘‘Notes on the Geography and Geology of Lake 
Huron. ’ This paper, published the following year at London, 
contains a description and figures of several species of straight- 
shelled cephalopods from Drummond and Thessalon islands in 
the north end of the lake. Of one genus Bigsby had only the 
siphuncles and it is not surprising that their actiniform lamellae 
led him to describe them as species of corals having “in their 
general appearance a considerable resemblance to vertebrae’’. 
Mr. Charles Stokes, a fellow of the Geological Society, undertook 
to name the supposed corals for Bigsby. He gave then the 
Uowa Geol. Surv., Vol. X, p. 454, also Vol. VIII, pp. 152 and 158. 
2Iowa Geol. Surv., Vol. XVI, p. 616. 
sSee Chamberlin and Salisbury, “Introductory Geology,” 1914, p. 390 or 
Charles Schuchert, “Paleogeography of North America,” Bull. G. S. A., 1910, 
Plate 67. 
^Trans. Geol. Soc. London, second series, Vol. i, pt. ii, pp. 175-209, Plates 
XXV, xxvi, xxviii, xxx. 
