Oonoceras, from the Upper Silurian of Europe, Russia and possibly North America. Oocerina differs primarily in having an actinosiphonate siphuncle composed of numuloidal (beaded) segments. Paroocerina (K288), named by Zhurevleva in 1961, is a slender oncoceratid from the Middle and Upper Silurian of eastern Europe and ex-USSR (Russia), similar to Oocerina, but with a hyponomic sinus. The genotypes of Oocerina and Paroocerina, respectively O.lentigratum and P. podolskensis, are from the Upper Silurian of central Europe and Russia Relationships A close relationship can be inferred between Loganoceras and Romingoceras and between Dunleithoceras and Richardsonoceras from the Middle and Upper Ordovician of North America as they are respectively from the same area from the same time. Ehlersoceras seems to stand more alone. A close relationship may also be inferred between the primarily Silurian genera from Europe, including Russia; Oonoceras, Oocerina and Paroocerina, which are very similar in overall form. The slender type oncoceratids give way to the strongly compressed Digenuoceras with sharply acute dorsum and venter, and to the more conical Miamiceras and Rizoceras. References Walter C.Sweet, Nautiloidea-Oncocerida, in the Treatise on Invertebrate Paleontology, Part K, Teichert C and Moore R.C Eds, Geological Society of America and University of Kansas press, 1964 (K283-K290) Nautiloids Middle Ordovician first appearances Silurian extinctions