What is "ammagnostidae"

Ammagnostidae is a family of trilobites in the suborder Agnostina, small, eyeless, isopygous trilobites with a thorax consisting of 2 segments only. Four genera have been assigned to it:

Ammagnostus Öpik, 1967

• Ammagnostus psammius Öpik, 1967 ( Type)
• Ammagnostus bassus (Öpik, 1967)
• Ammagnostus bella Guo & Luo, 1996
• Ammagnostus beltensis (Lochman, 1944)
• Ammagnostus cryptus
• Ammagnostus cylindratus Guo & Luo, 1996
• Ammagnostus duibianensis Lu & Lin, 1989
• Ammagnostus histus
• Ammagnostus hunanensis
• Ammagnostus integriceps Öpik, 1967
• Ammagnostus laiwuensis (Lorenz, 1906)
• Ammagnostus mitis Öpik, 1967
• Ammagnostus sinensis Peng, 1987
• Ammagnostus wangcunensis Peng & Robison

Hadragnostus Öpik, 1967

• Hadragnostus las Öpik, 1967 ( Type)
• Hadragnostus edax Fortey & Rushton, 1976
• Hadragnostus helixensis Jago & Cooper, 2005
• Hadragnostus modestus (Lochman, 1944)

Kormagnostus Resser, 1938

• Kormagnostus sinplex Resser, 1938 ( Type)
• Kormagnostus boltoni Westrop et al., 1996
• Kormagnostus copelandi Westrop et al., 1996
• Kormagnostus flati Pratt, 1992
• Kormagnostus inventus Shergold, 1982
• Kormagnostus minutus (Schrank, 1975)
• Kormagnostus seclusus ( Walcott, 1884)

Proagnostus Butts, 1926

• Proagnostus bulbus Butts, 1926 ( Type)
• Proagnostus centerensis Resser, 1938
• Proagnostus maryvillensis Resser

They lived during the late Cambrian period to the Ordovician period.