Diagnostic characters
Shell covered with thick periostracum marked with prosocline ridges; whorls tumid and sutures deep. Some shells show slight spiral ridges at periphery of last whorl under periostracum. Aperture large, squarish. Umbilicus usually absent but sometimes a chink is present. Animal with two tentacles under operculum.
Other characters
The shell is rather solid, with 6-7 whorls forming a high spire with a stepped profile. If there is no umbilicus a columellar groove is not obvious, though it is when an umbilical chink occurs. The base of the aperture is drawn out to form a distinct spout. Yellow or brownish. Up to 14mm high. 10mm broad; last whorl occupies 75% of shell height, aperture 45-50%,
The body of the animal is like that of L. vincta, is pale yellow, dark on the dorsal surface of the snout. The metapodial tentacles are white.
L. crassior is uncommon. It is usually found on soft bottoms from L.W.S.T. to depths of 90m, and has been recorded off many British and Irish coasts; commoner in the north since its main distribution is arctic. It is said to feed on the bryozoan Alcyonidium gelatinosum; its life-history is not known. It has sometimes been regarded as merely a deep water form of L. vincta.