46 THE AMERICAN NATURALIST. [VoL. XXXV. 
different species and at different times, in which case the 
genus would still be strictly monophyletic. But in the case 
where the resemblance is merely that of shape and not of 
development, as in the several species of Scaphites, the genus 
is not monophyletic, and the forms of which the development 
is different from that of the type cannot strictly be placed in 
that genus. | 
Baculites probably originated from Lytoceras, but it is not 
at all likely that all species of Baculites came from the same 
parent Lytoceras, nor, indeed, in the same region, for this 
degenerate form is too widely distributed and too short lived 
geologically for this to be probable. This supposition would 
presuppose for Baculites means of distribution surpassing those 
of the other invertebrates, which we know could not have been 
the case, for they were not pelagic forms, but shore dwellers, 
and individual species are no more widely distributed than the 
gastropods and pelecypods that are associated with them. 
STANFORD UNIVERSITY, CALIFORNIA. 
