Technically either form (Athrys’s or Athrys’) is acceptable as Athrys is a singular noun rather than plural (in which case the apostrophe without the following S would be correct). A quick Google search will return several websites stating this, but here’s a quote from a blog on Grammarly (emphasis added to distinguish examples): [quote]Style guides vary in their recommendations of what to do when you have a singular proper noun that ends in s. Some recommend adding only an apostrophe: [i]Charles Dickens’ novels Kansas’ main airport[/i] Others say to add apostrophe+s: [i]Charles Dickens’s novels Kansas’s main airport[/i] No matter which style guide you use, add only the apostrophe to plural proper nouns that end in s: [i]The Harrises’ house The Smiths’ vacation[/i] Use whichever style matches the style guide you use for your writing. If you don’t have a style guide, it’s OK to just pick one of the methods, as long as you don’t switch back and forth within the same document.[/quote] (The full text of the page can be found here https://www.grammarly.com/blog/apostrophe/ ) Essentially, so long as the writers of D2 use the same form in similar situations they’re fine. (΄◉◞౪◟◉｀)