No. 409.] THE LARVAL COIL OF BACULITES. 4I 
chambers of the larval coil, indicating a persistence of embryonic 
characters. This persistence of the siphonal czecum is seen in 
the young of Lytoceras alamedense! from the same locality, and 
it is interesting to note that this species of Lytoceras shows 
degeneration also in the development of its septa; the genus 
normally has its lobes trizenidian (three-pointed) in the early 
adolescent stages, while at maturity they always become dicra- 
nidian (divided into two sections); but Z. a/amedense never has 
trizenidian lobes, they being dicranidian at the beginning of the 
adolescent stage. In Lytoceras we have an early inheritance 
of a mature character, and in Baculites a similar prematurity 
of development, but accompanied by greater retardation. In 
Lytoceras alamedense the septa become ammonitic at one 
and five-twelfths coils, diameter 1.87 mm., while in Baculites 
chicoensis the septa persist in the goniatite stage until the shaft 
has extended two and a half millimeters from the larval coil, 
corresponding to nearly two revolutions if the shell had been 
coiled continuously in a spiral. 
Another mark of retrogression is the contraction of the 
whorl in the latter part of the larval coil; in the early stages 
the whorl increases normally in size, but at about three-fourths 
of a revolution begins to contract, until where the shaft leaves 
the coil it is much more slender than the embryonic or earlier 
larval whorl, and does not attain its former size until it has 
grown some distance beyond the coil. Contraction or abnor- 
mal shape of later whorls in ammonites has been shown by 
J. F. Pompeckj? to be a manifestation of degeneration, and to 
be accompanied by an early extinction of the race. In Baculites 
we find the contraction of the chamber pushed back by tachy- 
genesis into the larval stage, and a profound degeneration 
otherwise shown; from the geological history of the race we 
know that its life was short and that extinction speedily followed 
upon this unnatural development of the shell. 
Ontogeny of Baculites. — At maturity Baculites chicoensis 
consists of a straight shaft, slightly tapering, with an ovoid 
1 Smith, J. P. Proc. Cal. Acad. Sci., third series, Geology, vol. i, No. 4, 
Pl. XVI, Fig. $ 
? Die Ammonoideen mit Anormaler Wohnkammer. 1894. 
