330 



PALEONTOLOGY OF NEW YORK. 



tions, which are usually present in the valves of the deltidiuni- bearing species, 

 such as Leptcma rhomhoidalis, Choneles scitula, etc., do not exist in the deltidiuni.* 



Flo. 288. 



FlQ. 261. 



Fio. 263. 



Fig. 280. 



Fig. 282. 

 CUtella KeapolUana. 



Fio. 264. 



Tig. 259. The completed cephalula-etage. 



Fig. 260. LoDgUudinal section of 8amc; the shcll-socretlng earfaces are represented by heavy lines. 



Tig. 261. Tlio larva after inversion of the mantle lobes. 



Tig. 263. Longitadinal section based on the preceding. The shell-bearing snrfaoes are now on the ontside of the 



anim.il, the largo pedicle extending upward. 

 Figs. 263, 201. Dorsal and profile views of a very young shell; showing the large posterior opening between the 



▼alves and the thick pedicle. 



(Beeciier ; adapted from Kowalevski and Shiplet.) 



In the corresponding stages of growth in Cistella and Terebr.4tolina, there 

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

 dium, 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 Tebebratulina and Magellania 

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



* In AuLOBTBOBa the surface of tbe deltidium is covered with short spinules or tubercles. Such spinules 

 in the productoids imply a punctation of the shell, wherever occuningf on the valves, but an examination 

 of the deUi<lium in this ^nus indicates that the secondai-y modification of the surface of the deltidium is not 

 accompanied with a punctate structure. 



