330 



PALEONTOLOGY OF NEW YORK. 



tions, which are usually present in the valves of the deltidiuni-l)earing species, 

 such as Lepkena rhomboidalis, Chonetes scitula, etc., do not exist in the deltidiuni.* 



Fig. 259. 



riG. 261. 



Fig. 263. 



Fig. 260. 



Fig. 262. 

 Cistella NeapoKtana. 



Fig. 264. 



Fig. 259. The complele'l oephalula-stage. 



Fig. 260. LoDgUudinal .section of same; the shell-secreling surfaces are represented by heavy lines. 



Fig. 261. The larva after inversion of the mantle lobes. 



Ftg. 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, 204. Dorsal and profile views of a very young shell; showing the large posterior opening between the 



valves and the thick pedicle. 



(Beeciiek -, adapted from Kowalevski and Shipley.) 



In the corresponding stages of growth in Cistell.v and TeREBR.iTULiNA, there 

 is no evidence of this body-plate, no indication in any growth-stage of a delti- 

 diuni, 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 Terebiiatulina and Magellania 

 in which the deltaria have become more or less completely developed, it has been 



*In Aolosteges the surface of the ileltidium is coveretl with short spinules or tubercles. Such spinules 

 in the jiroductoids imply a punctation of the shell, wherever occurring- on the valves, but an examination 

 of the deltiiliura in thi.s g-enus indicates that the secondary modification of the surface of the deltidium is not 

 accompanied with a punctate structure. 



