that portion of it which constitutes the unduloid, has not grown by successive {571} increments or ãrings of growth,ã but has developed as a whole.) A thickened ãribã is often, perhaps generally, present on the dorsal side of the little conical shell. In a few cases (Limacina, Peraclis) the tube becomes spirally coiled, in a normal logarithmic spiral or helico-spiral.
In certain cases (e.g. Cleodora, Hyalaea) the tube or cone is curiously modified. In the first place,