330 
PALEONTOLOGY OF NEW YORK. 
tions, which are usually present in the valves of the deltidium-bearing species, 
such as Leptce,na rhomhoidalis, Chonetes scitula, etc., do not exist in the deltidium.* 
Fig. 259. 
Fig. 261. 
Fig. 263, 
Fig. 262. 
Cistella NeapoUtana. 
Fig. 264. 
Fig. 259. The completed cephaliila-stage. 
Fig. 260. Longitudinal section of same; the shell-secreting surfaces are represented by heavy lines. 
Fig. 261. The larva after inversion of the mantle lobes. 
Fig. 262. Longitudinal section based on the preceding. The shell-bearing surfaces are now on the outside of the 
animal, the large pedicle extending upward. 
Figs. 263, 264. Dorsal and profile views of a very 3mung shell; showing the large posterior opening between the 
valves and the thick pedicle. 
(Beecher ; adapted from Kowalevski and Shipley.) 
In the corresponding stages of growth in Cestella and Terebratulina, there 
is no evidence of this body-plate, no indication in any growth-stage of a delti- 
diurn, but the pedicle-passage formed by the ultimate union of the valves at 
their cardinal extremities remains uncovered until a comparatively late stage. 
By removing the shell from adult specimens of Terebratulina and Magellania 
in which the deltaria have become more or less completely developed, it has been 
* In Aulosteges the surface of the deltidium is covered with short spinules or tubercles. Such spinules 
in the productoids imply a punctation of the shell, wherever occurring' on the valves, but an examination 
of the deltidium in (his genus indicates that the secondary modification of the surface of the deltidium is not 
accompanied with a punctate structure. 
