a seashells is a mean of preposition
clamshell is not thoracotomy. clamshell is thoracotomy. spatial_preposition is preposition. seashell is not shell. atelic_directional_preposition is spatial_preposition. atelic_directional_preposition is not spatial_preposition. preposition_of is preposition. seashell is shell. topshell is not trochus. spatial_preposition is not preposition.