A Grammatical Dictionary of Botanical Latin

Subclass: subclassis,-is (s.f.III), dat. sg. subclassi, abl. sg. subclasse, nom. & acc. pl. subclasses, gen. pl. subclassium, dat. & abl. pl. subclassibus.

- species nova ab omnibus aliis speciebus suae subclassis foliis ellipticis differt, the new species from all other species of its own subclass differs by the elliptic leaves.

- subclassis nova a subclasse Archidiidis distincta, new subclass distinct from the subclass Archidiidae.

NOTE: a noun used to describe another, and denoting the same person or thing, agrees with it in case: e.g. above: subclasse (abl.) and Archidiidis (abl.) even though one is a singular and the other a plural noun.

  Subclassis,-is (s.f.III; an i-stem noun),     -idae (pl.f.)
        sg.          pl.
Nom. subclassis  subclasses           Archidiidae   Archidiidae
Gen. subclassis  subCLASSIUM          Archidiidarum Archidiidarum
Dat. subclassi   subclassibus         Archidiidis   Archidiidis
Acc. subclassem  subclasses           Archidiidas   Archidiidas
Abl. subclasse   subclassibus         Archidiis     Archidiidis

According to the Code of Nomenclature (Vienna 2006) (recommendation 16A:

Latin endings for the rank of Class and Subclass are:

 1. for Algae:  CLASS:    -phyceae,   gen. pl. -phycetarum (pl.f.I)