Serrated Mesogondolella (Jinogondolella) have a limited distribution; though they dominate West Texas and some China faunas, they are rare in open-sea deposits of the Tethys. It appears they preferred semi-restrictive (saline) basins. The carbonates associated with a volcanic edifice (atoll) displayed in Oman represent a mixture of open-sea and restrictive basins deposits and contain the conodont index species of the type Wordian in the Delaware basin, M. aserrata, along with the common Tethyan form, M. siciliensis, and abundant Tethyan ammonoids. The well preserved ammonoids have long been correlated with the classic ammonoid fauna from Rupe del Passo di Burgio in Sosio Valley, Sicily, and with the Wordian. The co-occurrence of a contemporaneous Sosio ammonoid fauna with that of Tethyan and West Texas conodonts is a keystone for correlation. It allows the following conclusions: (1) The famous Sosio ammonoid faunas and contemporaneous faunas of Oman are precisely correlated to the Wordian of West Texas by their co-occurrence with M. aserrata. The Wordian in West Texas is now defined as the range of M. aserrata. (2) Lower Midian fusulinid faunas of the Tethys (found in Sosio) can be assigned to the (upper) Wordian. (3) Further, Sosio type ammonoid and lower Midian fusulinid faunas, present in the entire Tethys, can be used as markers for the Wordian. (4) Mesogondolella siciliensis is the dominating species of Tethyan Wordian conodont faunas. (5) M. siciliensis ranges from middle Roadian to upper Wordian. (6) Wordian conodont faunas can be characterized by the smooth species M. siliciensis in the Tethyan province and by the serrated species M. aserrata in the Ouachita-Cathaysia province.