Shell closely related to I. pharcida with which it may advantageously he compared. The most obvious differences are, that in I. pharcida the ribs and their intersecting sharp spirals are as strong on the last whorl as on the others, in I. acrybia the ribs on the last whorl are obsolete and the spirals fainter; the spire of I. acrybia is shorter in proportion to the last whorl, the canal is longer, there is one less whorl in the adult shell, the fasciole is less excavated, the suture more appressed, and consequently less evident. In all other respects the shells closely resemble one another. Lon. of shell, 10.0 mm; of last whorl, 6.0 mm; of aperture, 4.0 ; max. lat. of shell, 4.0 mm. The same measurements in I. pharcida, of the same maturity, are, lon. of shell, 11.75 mm; of last whorl, 6.25 mm ; of aperture, 4.5 mm; max. lat. of shell, 4.0 mm.
NOT FIGURED

USA. Florida. Off Fernandina.