No. 409.] THE LARVAL.COIL OF BACULITES. 49 
EXPLANATION OF PLATES. 
The Development of the Larval Coil of ZacuZites chicoensis Trask. 
Fics. 1 and 2. Protoconch, front and top view, diameter 0.48 mm. Thirty 
times enlarged. 
IG. First or ananepionic septum, showing the siphonal caecum. 
Fics. 4 and 5. Larval shell at one-fourth coil, diameter o. 58 mm., showing the 
ananepionic and metanepionic septa, and the embryonic constriction. Thirty 
times enlarged. 
FIG Second or metanepionic septum, at one-fourth revolution, diameter 
0.58 mm 
Fics. 7 and 8. Larval shell at one-half coil, diameter 0.68 mm. Thirty times 
enlarged. 
Fic. 9. Sixth septum, at one-half revolution. 
Fics. r0 and 11. Ananepionic shell, showing the embryonic constriction, the 
ananepionic septum, the siphonal caecum, and the first larval body chambe 
he yo animal died before further development took place. Thirty times 
enlarge 
Ananepionic shell showing ornamentation of the embryonic and 
early larval shell, and the ananepionic body chamber. Thirty times enlarged. 
d r4. Metanepionic shell at three-quarters of a coil, diameter 0.83 
mm., showing contraction of the later chambers 
FiGs. 15 and 16. Shell at end of the caress stage, diameter 1.06 mm., 
one and one-eighth coils. Thirty times enlarge 
Fic. 17. Metanepionic shell, diameter 1.00 mm., showing periodic swelling of 
the siphuncle, indicating a retardation of the phylembryonic siphonal caecum. 
Thirty times enlarged. 
Fic. 18. Larval coil attached to the straight shaft, showing all the stages from 
phylembryonic through the paranepionic, and the beginning of the adolescent or 
neanic stage. "Ten times enlarged. 
Fics. 19 and 20. Front and side view of a metaneanic shell, showing the 
unsymmetric shape of the larval coil, and the contraction of the metanepionic 
body chamber. Thirty times enlar 
Fic. 21. Composite specimen, Peta from several pieces, showing the aui 
ment of the septa from the ananepionic into the adolescent stage. Ten tim 
enlarged. 
Mo.Bot. Garden, 
1902. 
