THE AMERICAN NATURALIST. [Vol. XXXVII. 



able reports of the alleged finding of these shells in other regions, 

 we find their geographical range in modern as well as Tertiary 

 times to be along the Atlantic coast 

 of North America, from the south 

 shore of Cape Cod, to the Gulf of 

 Mexico. The peculiarly restricted 

 distribution of this group is explained 

 by the fact, that the animal on leaving 

 the egg capsule is without a velum. 

 This latter, though well developed 

 and large before hatching, (see Figs, 

 i and 2) is dropped just before the 

 ' \ [\ 'en, d„m " t i ',' J'm i', -uh' 1 anmia l emerges from the capsule, and 

 showing the shell, giiis, heart, and a fter the shell is already well devel- 

 oped. Thus the meroplanktonic 

 stage, which we may assume existed in the ancestors of Fulgur 

 and Sycotypus, was apparently suppressed even in the earliest 

 species of Fulgur, as otherwise the distribution would be more 

 world-wide. Actual migration is prevented by the differences 

 in temperature of the water and by the ocean currents. This 

 condition of affairs has existed in this region in all probability 

 since Miocene times. 



