4. Limacina. One species.

Shell papyraceous, very fragile, planorbis form, sub-carinated,

involuted rather obliquely, in such a manner as to be deeply and largely

umbilicated on one side, and the spine slightly projecting and pointed

on the other; aperture large, entire.

_L. helicialis._ The Helix-like Limacina.

Thin, fragile, spiral; the volutions united in a discoid form.