Which form of estate does not allow for sale or transfer beyond a specified line of heirs?

A Fee Tail is a form of estate that restricts inheritance to a specific line of heirs, typically the direct descendants of the original owner. In this type of estate, the property can only be passed down to designated heirs, and if those heirs do not exist or if no direct descendants are available, then the estate cannot be sold or transferred beyond that specified line of heirs. This limitation is a key characteristic of Fee Tail estates.

In contrast, a Life Estate allows the property to be used for the lifetime of the individual but does not restrict the sale or transfer of the property during that individual's life, although it reverts to another party upon their death. A Fee Simple Defeasible can be sold or transferred, but it carries conditions that could lead to its termination, rather than restricting inheritance strictly to heirs. A Leasehold Estate involves renting rather than ownership transfer and does not have the same restrictions as a Fee Tail, as it is not an ownership interest in the same sense.

Thus, the unique limitation on the transfer and sale of property specifically to certain heirs identifies the Fee Tail as the correct answer.