"' Hemiphragmoceratidae "'is a family of endogastrically brevconic oncocerids characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients . ( Sweet 1964, Flower 1950 ).
32.
The family has its beginning with the Middle Silurian " "'Protophragmoceras " "', known from a gradually and evenly expanding endogastric shell with an unrestricted aperture, like that of ts cyrtogomphoceratid ancestors, deep sharp hyponomic sinus for the water-jet funnel, and ventral siphuncle, phragmoceratid in character.
33.
Growth lines are sinuous, show a pronounced hyponomic sinus in the coiled juvenile portion at the apex but almost none at the mature aperture of the orthcone . " Holmiceras " is similar except that its whorls are more loosely coiled and it is known only from the Arenigian whereas " Ancistroceras " ranges through most of the Middle Ordovician.
34.
Members of the Poterioceratidae are distinguished by a subcircular to compressed exogastric shell ( curved upwardly so as the lower side, the venter, is convex viewed from the side ) that has no hyponomic sinus and a central to subcentral siphuncle composed of subquadrate to nummuloidal segments in which the septal necks are more strongly curved on the upper, or dorsal side.
35.
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.
