The shell is thick, imperforate (no umbilicus), and usually has flat, spiral ribs.
When a liquid is to be separated from a liquid, the receptacle must be imperforate.
The 2nd or 1851 issue, as it is called in the circular, actually consisted of two series, the imperforate and perforate.
Although made and approved, this stamp is said to have been withheld from issue in this imperforate condition.
The inverse ratio of seven to one for a catalogue value would make the perforated stamp list $42 with the imperforate at $6.
Attempts are, however, made to palm off trimmed reprints as imperforate specimens.
The 1c in coil form was also issued with the 12 perforation at top and bottom and imperforate at the sides.
The stamp is nearly square, and the specimens possessed by our correspondent are imperforate.
The first stamps were imperforate, necessitating the use of scissors or other instrument in separating them.
A range of the early penny red stamps, from the imperforate red-brown stamp of 1841 to the Die II.
imperforate im·per·fo·rate (ĭm-pûr'fər-ĭt)
Lacking a normal opening.