234 Tin American (ienlaijisl. October, 1893 
siderable local interest, it is extremely doubtful how far general 
science is benefitted by their publication. The frequent im- 
possibility of identifying such previously described forms 
with the much more perfect material found later elsewhere, 
simply leads to a confusion in the terminology of the genus, 
for all advance in actual knowledge must be based upon ma- 
terial with good superficial as well as interior characters. 
Though there is no hope for such a decision yet science would 
gain if only those species were recognized as having pri- 
ority, which were based upon surface as well as other char- 
acters, and which, for reasons I hope to show later, also in- 
clude a description of the siphuncles. 
It is especially among forms with smooth shells that dis- 
crimination between species often becomes well-nigh impos- 
sible. Under such circumstances it would seem as though al- 
most any character would be seized upon which could shed 
additional light upon the subject. In a general way this has 
been done in discriminating between the strongly annular 
siphuncle of the forms classified as Actinoceras, and the less 
annulated forms of Orthoceras. But there are other distinc- 
tions between the siphuncles of various species, which are 
capable of more specific application. One of these consists 
in the relation which the diameter of the siphuncle bears to 
the general diameter of the shell ; another, in the degree of 
convexity exhibited by the individual annulations of the 
siphuncle, taking account of all the variations between those 
with practically straight sides and the more convex ones. At 
times it is even serviceable to distinguish between species 
having the siphuncle regularly very eccentric, moderately so, 
or centra], and finally those in which the position of the 
siphuncle varies. It is a mistake to conclude that because 
sometimes in the same species the characters of the siphuncle 
vary considerably, no assistance can be gained from its 
examination. In some forms the characters of the siphuncle 
are remarkably constant and are of considerable value in as- 
sisting to discriminate between species. It is evident that 
these variations should be studied from numerous individuals 
of the same species, as, indeed, experience has taught us to do 
with the apical angle, the hight of chambers, and other 
features generally used for discrimination. In such a study 
