[1] Neuter nouns ending in -e, -al, -ar undergo the same change in the genitive plural as the i-stem nouns discussed in the previous post i.e. -ium, but they also have changes in the ablative singular [-ī] and nominative / accusative plural [-ia]; such nouns are few in number and not common.
From the authors:
[1] Eundem in exemplāria mīlle trānscrīptum per tōtam Ītaliam prōvinciāsque dīmīsit (Pliny) │ Then a thousand copies were written of the same memoir, which he dispersed through all of Italy and the provinces.
[2] Reliquī disseruērunt sine ūllō certō exemplārī fōrmāque reī pūblicae (Cicero) │ His successors have discussed the different types of State and their basic principles without any definite example or model
[3] in eō conclāvī ego perfōdī parietem (Plautus) │ in that same room I have dug a hole through the party-wall
[4] Etiam rogitās, scelestē homō, quī angulōs in omnīs meārum aedium et conclāvium mihi pervium facitis? (Plautus) │ Do you even ask me, you rascally fellow? You who've been making a thoroughfare of every corner of my house, and the rooms under lock and key? (conclāve can refer to a room that is locked)
Note: aedis, aedis [3/f]: [i] temple, shrine [ii] plural (aedēs): house; i-stem noun (the same number of syllables in the nominative and genitive singular)
[5] absolūtum offendī in aedibus tuīs tēctum, quod suprā conclāvia nōn placuerat tibi esse multōrum fastīgiōrum, id nunc honestē vergit in tēctum īnferiōris porticūs (Cicero) │ I found the roof on your house finished: the part over the sitting-rooms, which you did not wish to have many gables, now slopes gracefully towards the roof of the lower colonnade.
[6] repente glōriāns maria montīsque pollicērī coepit (Sallust) │ suddenly, boasting, he began to promise her seas and mountains
Note: montīs, the alternative accusative plural of the i-stem noun
[7] Quōs vōs implōrāre dēbētis ut … hanc omnibus hostium cōpiīs terrā marīque superātīs ā perditissimōrum cīvium nefāriō scelere dēfendant (Cicero) │ You ought to implore them … with all the forces of the enemy having been overcome on land and (on) sea, that they defend her from this wicked crime of the most dangerous citizens.
[8] Columella on the management of chickens …
Plūrimī etiam īnfrā cubīlium strāmenta grāminis aliquid et rāmulōs laurī │ Very many people also lay a little grass under the litter of the nest-boxes and small branches of bay
[9] Celsus on, well, read it for yourself …
perīculōsa etiam, quae inter febrēs fluēns conquiēscere hominem in cubīlī nōn patitur (Celsus) │ it is dangerous also during fevers when fluid stools allow the patient no rest in bed
[10] Celsus on being bitten …
Dīxī dē iīs vulneribus, quae maximē per tēla īnferuntur. Sequitur, ut dē iīs dīcam, quae morsū fīunt, interdum hominis, interdum sīmiae, saepe canis, nōnnumquam ferōrum animālium aut serpentium │ I have spoken of those wounds which are mostly inflicted by weapons. My next task is to speak of those which are caused by the bite, at times of a man, at times of an ape, often of a dog, not infrequently of wild animals or of snakes.
serpēns, serpentis [3m/f]: snake; gen pl: serpentium or serpentum
This is a good example that leads us to the last point about i-stem nouns …
[2] Before we put this topic “to bed”, remember where we started: The i-declension was confused even to the Romans themselves, nor was it stable at all periods of the language (Allen & Greenough).
In Modern English there can be variations in, for example, plurals and verb forms and so it is not surprising to find slight variations in the Latin language that was used for centuries. In the grammar books, look out for words such as “occasionally” or “(very) rarely” because that is indicating that a form is attested i.e. it was used by an author but it does not frequently occur.
[i] You will come across:
different ablative singular endings for the same noun e.g. mare / marī; nāve / nāvī; colle / collī
different genitive plural endings for the same noun:
apis, apis [3/f]: bee; gen pl: apium or apum
serpēns, serpentis [3m/f]: snake; gen pl: serpentium or serpentum
mēnsis, mēnsis [3/m]: month; gen pl: mēnsium or mēnsum
[ii] a small group of 3rd declension i-stem nouns have an alternative accusative singular in -im
Nominative singular: turris, turris [3/f] tower
Accusative singular: turrim or turrem
Similarly:
febris, febris [3/f]: fever > accusative: febrim or febrem
puppis, puppis [3/f]: stern of a ship > accusative: puppim or puppem
[iii] Some forms are rare or, in fact not attested in Classical Latin, but are evident in later Latin:
Quandō māchinam per verbum suum fēcit Deus caelī, terrae, marium (Mediaeval)│ When by His Word, God made the system of heaven, earth, seas
Latin tutorial:
https://www.youtube.com/watch?v=jm8HjKvzpeE&t=216s
