No. 409.] THE LARVAL COIL OF BACULITES. 45 
B. compressus has two revolutions in its coil. But the develop- 
ment of the two species is essentially the same, and the genus 
is monophyletic, in so far as observations on two species can 
demonstrate it. Dr. Brown thought that the larval stages of 
Baculites showed analogy with those of Crioceras and Ancylo- 
ceras, and none with Scaphites. In all probability, however, 
all three of these genera are polyphyletic, and have originated 
from several stocks. Some species of Scaphites seem to come 
from a Hoplites-like ancestor, but in studying the development 
of some undescribed Scaphites from the upper Cretaceous of 
southern Oregon the writer found their larval stages to be 
very like those of Lytoceras and Baculites, and they probably 
have a common origin. 
Straight degenerate forms have appeared in the history of 
the cephalopods from time to time, from the Trias upward, not 
from any one stock in particular, and not genetically connected. 
The mere fact that the form is abnormal is no indication what- 
ever of kinship. In each case they spring from normal forms 
and indicate their origin in their normally coiled young. Natu- 
rally it is seldom that transitional forms from the progressive 
to the degenerate are known, for the beginnings of these tran- 
sitions are regarded as mere freaks of some normal species. 
Further, degeneration or retardation is not necessarily accom- 
panied by abnormality of form, as has been shown by the 
writer in the case of Lytoceras alamedense and in the develop- 
ment of Placenticeras,! where the genus is still progressive in 
many characters. Whether normal or abnormal in shape these 
degenerate forms are always short lived, for they represent the 
extreme specialization of which the group is capable, while the 
more primitive stocks or radicles persist through very long 
periods, often little changed, but from time to time giving rise 
to the abnormal forms as side branches. These side branches 
coming off from the parent stock at no great distance in time 
from each other may give the semblance of a genetic series, 
but this is usually deceptive. It is thus supposable that some 
of these forms have originated from the parent stock from 
1 The Development and Phylogeny of Placenticeras, Proc. Cal. Acad. Sci, 
third series, Geology, vol. i, No. 7, 1900. 
