Arpadites is a genus in the Ceratitid

Ceratitida

The Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites....

 family Arpaditidae from the Middle and Upper Triassic (Ladinian and Carnian stages) of the Alps, Italy, Balkans, Himalayas, and Japan. (Arkel et al 1962,L162)

Arpadites, named by Mojsisovics,,1879,is characterized by a compressed, evolute, discoidal shell with radial or faintly sigmoidal ribs; smooth, continuous keels; umbilical tubercles, with or without lateral and ventrolateral tubericles as well; and ceratitic sutures with two lateral lobes (on either side). The genotype Arpadites arpadis came from the upper Middle Triassic (Ladinean) of the Alps in Europe. (ibid)

References

• Arkel et al, 1962. Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology
  Treatise on Invertebrate Paleontology
  The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...
  
  Part L, Mollusca 4, R.C. Moore (ed)