from the USPS Postal Bulletin May 9, 2019:
Save Vanishing Species Semipostal Stamps Withdrawn From Sale — Statutory Authority Expired December 31, 2018

Effective close-of-business December 31, 2018, all Post Offices, stations, branches, and contract postal units were to withdraw from sale the Save Vanishing Species semipostal stamp stock (Item 576600). These items are to be retained at the unit level until further notice. Do not prepare these items for destruction at this time.

Absolutely no sales of the Save Vanishing Species semipostal stamps and products are permitted at retail counters and outlets. The items are also withdrawn from sale at Stamp Fulfillment Services and The Postal Store at usps.com/shop.