Specific Characters in Orthoceras. — Foerste. 235 
the relative width of the siphuncle, and the relative convex- 
ity of the individual annulations will also have their value. 
No specific description can be considered complete which 
doesn't also give the characters of the siphuncle and the ex- 
tent of its variations, for it has often happened that when 
internal characters have received their full share of attention, 
new light is cast upon their generic and specific distinc- 
tions. 
While studying the species of Orthoceras from the Clinton 
group a very interesting case of constancy under variation 
came to notice. At the bottom of the Clinton group in Huff- 
man's quarry, southeast of Dayton, Ohio, occurred at one place 
a white and very compact limestone full of various species of 
Orthoceras. In one of these species with a smooth shell, Or- 
thoceras erraticum Foerste, in all the fragments examined, the 
siphuncle below is distinctly annulate, and excentric. Above, 
it changes its position until it becomes more nearly central, 
and at about this point the siphuncle begins to change its 
character and to become more nearly cylindrical. Higher up 
the siphuncle becomes excentric again, but towards the other 
side of the shell still retaining its cylindrical character. The 
case has seemed so interesting that the three largest fragments 
are here figured. In 1 the change of position of the siphuncle 
is not noted because the section passes vertical to the plane of 
the curvature of the siphuncle, but the cylindrical character 
of the upper annulations is well seen. In 2, the change of 
position is well seen, and the cylindrical character of the up- 
per annulations would be more distinct if the section had 
passed a little deeper at this end. In 3, the upper portion 
with the more cylindrical annulations is evidently broken off, 
although the beginning of the change can be noted. Here is 
an instructive instance of variation within the limits of the 
same species, which may even afford some lessons in the 
development of the group. It has been noted in one Clinton 
and some earlier forms that in those species which have the 
annular character most strongly developed, i. e., Actinoceras, a 
smooth exterior shell generally prevails. In that case the 
more typical forms of Orthoceras with a cylindrical siphuncle 
may be considered as a later development and the species here 
figured might be cited as a case in which such a change was 
