_Sing._ _Plur._ | _Sing._ _Plur._ Animalcul-um animalcul-a | Mausole-um mausole-a Arcan-um arcan-a | Medi-um medi-a Collyri-um collyri-a | Memorand-um memorand-a Dat-um dat-a | Menstru-um menstru-a Desiderat-um desiderat-a | Moment-um moment-a Effluvi-um effluvi-a | Premi-um premi-a Empori-um empori-a | Scholi-um scholi-a Encomi-um encomi-a | Spectr-um spectr-a Errat-um errat-a | Specul-um specul-a Gymnasi-um gymnasi-a | Strat-um strat-a Lixivi-um lixivi-a | Succedane-um succedane-a. Lustr-um lustr-a | (d).--_Where the singular termination -is is changed in the plural into -es_:-- _Sing._ _Plur._ | _Sing._ _Plur._ Amanuens-is amanuens-es | Ellips-is ellips-es Analys-is analys-es | Emphas-is emphas-es Antithes-is antithes-es | Hypothes-is hypothes-es Ax-is ax-es | Oas-is oas-es Bas-is bas-es | Parenthes-is parenthes-es Cris-is cris-es | Synthes-is synthes-es Diæres-is diæres-es | Thes-is thes-es. THIRD CLASS. _Words wherein the plural is formed by inserting -e between the last two sounds of the singular, so that the former number always contains a syllable more than the latter:--_ _Sing._ _Plur._ Apex _sounded_ apec-s apices Appendix -- appendic-s appendices Calix -- calic-s calices Cicatrix -- cicatric-s cicatrices Helix -- helic-s helices Index -- indec-s indices Radix -- radic-s radices Vertex -- vertec-s vertices Vortex -- vortec-s vortices. In all these words the c of the singular number is sounded as k; of the plural, as s. § 82. The following is a list of the chief Greek substantives lately introduced, and preserving the _Greek_ plural forms-- FIRST CLASS. _Words where the singular termination -on is changed in the plural into -a_:-- _Sing._ _Plur._ _Sing._ _Plur._ Apheli-on apheli-a Criteri-on criteri-a Periheli-on periheli-a Ephemer-on ephemer-a Automat-on automat-a Phænomen-on phænomen-a. SECOND CLASS. _Words where the plural is formed from the original root by adding either -es or -a, but where the singular rejects the last letter of the original root._ _Plurals in_ -es:--