THE LARVAL COIL OF BACULITES. 
JAMES PERRIN SMITH. 
Historical. — The genus Baculites is widely distributed in 
Cretaceous rotks, found in almost every region, and the straight 
shafts of this form are locally among the commonest fossils. 
But in nearly all these places only the straight, incomplete 
specimens are found; so that until a few years ago Baculites 
was supposed to be an ammonite that had reverted to the 
orthoceran form. About ten years ago, however, Dr. Amos 
Brown discovered in the Cretaceous beds of Dakota a number 
of young specimens of Baculites compressus, with a larval coil 
attached to the straight shaft; this he rightly interpreted as 
indicating the descent of Baculites from a coiled ancestor. 
Until recently the larval coil of Baculites had been found 
only at this single locality near Deadwood, Dakota; but during 
the past year the writer discovered a number of larval coils 
of Baculites chicoensis Trask in the lower Chico beds, Upper 
Cretaceous, on the Arroyo del Vallé, about eight miles south- 
east of Livermore, Alameda County, California. Many of the 
specimens are perfectly preserved, some with the shell on and 
others in clear, transparent calcite casts, showing the develop- 
ment and the specific characters as well as when the animal 
was alive. In order that the early stages of the shell should 
be preserved the animal must have died in early youth, for the 
test is too thin and delicate to have remained uninjured while 
attached to the larger shell, and not protected by it. All 
specimens more than a few millimeters in length are found 
with the small end broken off, as it could not have been of any 
use to the animal. ; 
A peculiarly fine sediment is necessary for the preservation 
of these fragile forms, and they were found only in calcareous 
nodules, where the amount of lime in the clay prevented the 
dissolving of the calcite of the shells, and where rapid hardening 
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