If it's an old synonym, it often won't be listed in the Catalogue of Life. The Plant List calls it a synonym of Mammillaria polythele.
http://www.theplantlist.org/tp...
We do have an entry for that one because it is recognized as an accepted species name by the CoL
Biznaga con Muchos Tuberculos (Mammillaria polythele)
We also have an entry for Neomammillaria crodidata:
Some of our entries were copied from The Plant List in the early days of our database, but I'm not certain that these species still exist. The CoL does list a few Neomammillaria species, but only as synonyms of Mammillaria species. The genus may no longer exist.
