40 THE AMERICAN NATURALIST. [VoL. XXXV. 
prevented their decaying or being ground up by the waves. 
The young must have flocked together in quiet nooks where 
the water was clear and where there was little grinding by wave 
action on sands or pebbles. Such concurrence of circumstances 
must necessarily be seldom found, and it is not surprising that 
these delicate forms have been found in only two localities in 
the world. 
Retardation in Baculites. — This genus has always been 
taken as a type of reversionary forms, since, although it 
descended from coiled ancestors, at maturity it resembles 
Orthoceras in its straight shell. It is, however, not really 
reversionary, for the septa are not orthoceran, nor even nau- 
tilian; they are ammonitic and complex, and grow more so 
towards maturity, after passing through a goniatite stage in 
early youth. The shell cannot, then, be said to have reverted to 
the stage of Orthoceras nor even of Bactrites ; but it is clearly 
a degenerate, retrogressive form, retarded in most characters, 
while progressive in others. Its septa fail to reach the degree 
of complexity attained by its not very remote ancestors; the 
number of lobes and saddles is reduced, and the goniatite stage 
is prolonged, the ammonitic stage being reached later in life 
than was the case with its immediate ancestors. 
But even this reduction of the elements of the septa responds 
to the law of tachygenesis and is pushed back in the ontogeny, 
so that in the earliest larval stages the full number of lobes 
and saddles is never present. Also the early straightening 
out of the spiral coil is progressive degeneration from a lytoce- 
ran form. In the genus Lytoceras it has often been observed 
that in old age the body chamber leaves the spiral a little way, 
and Baculites is merely a case of inherited senile degeneration, 
pushed back in individual ontogeny until the retrogressive 
characters appear at successively earlier stages of growth, 
reaching finally the larval stages. This is necessarily followed 
shortly by the extinction of the race. 
In all normal ammonites the siphuncle begins in the embry- 
onic protoconch with a caecum or bulbous enlargement, which 
never appears in later stages. Baculites shows retardation in 
its development by a repetition of the siphonal czecum in several 
