Hi Linda, This is not a matter of noun vs. adjective. The first thing to know is that a final "i" on a species name indicates the species was named after a man (an "ae" ending indicates it was named after a woman). When a species is named after a person, the specific name is formed by adding the "i" or "ae" suffix to the person's name. The double "i" ending can occur for a couple of reasons. First, if the man's name already ends in "i", then the additional "i" added to form the specific name will result in a double "i". A species named after Mr. Martin from the USA would be called martini, but one named after Mr. Martini from Italy would be martinii. Many of the double i's seen on species names however, date back to the 18th century or thereabout, when it was a popular custom for professional men like doctors, lawyers, professors, scientists, etc. to latinize their surnames. This resulted in many names ending in "i" which otherwise would not have, and because these individuals were prominent academics, many species were named after them. A few names are found both ways, for example, the frequently seen name Sowerby. There are quite a few species named sowerbyi, but there are also species named after the latinized form - sowerbii; and even a few names created by latin purists who replaced the "w" in his name with "v" - soverbii. Paul M.