§ 6-2.1 Estates in severalty, joint tenancy, tenancy by the entirety and in common Estates as to the number of persons owning an interest therein are classified as follows:

(1) In severalty.

(2) Joint tenancy.

(3) Tenancy in common.

(4) Only as to real property and, on and after January first, nineteen hundred ninety-six, as to the shares of stock of a cooperative apartment corporation allocated to an apartment or unit together with the appurtenant proprietary lease, tenancy by the entirety.