Here is the so-called Fir Bolgs part of the Book of Invasions.
§48. Now as for the Fir Bolg, they brought five chiefs with them, as above, namely, Gann, Genann, Rudraige, Sengann, Slanga: these were the five sons of Dela. Their five wives then, Anust, Liber, Cnucha, Fuat, Etar:
So it is said,
Fuat, wife of Slanga, don't think it's wrong,
Etar wife of Gann the brave,
Anust Sengann's wife with the spears,
Cnucha who was the wife of pure Genann.
Liber wife of Rudraige from the road,
A gentle people, who were not narrow:
Rudraige, master of tricks,
I guess, Fuat was his wife.
§49. The Fir Bolgs split into three. With Slanga f. Dela f. Lot his third in Inber Slaine: his province of Inn Colptha in Comar Tri nUisce; a thousand men his contingent. The second third landed at Inber Dubglaisi with Gann and Sengann: two thousand were their contingent, Gann from Comar Tri nUisce to Belach Conglais, Sengann from Belach Conglais to Luimneach - that is to say, on the two provinces of Mumu. Genann and Rudraige with a third of the army, they landed at Domnann: hence their name of Fir Domnann. Genann it is he who was king over the province of Medb and Ailell; Rudraige over the province of Conchobor - two thousand more were his contingent. These were the Fir Bolg, the Fir Domnann, and the Gailioin.
As for the Fir Domnanns, the cove takes its name from them. The Fir Bolg - they were named after their bags. The Gailioin, from the multitude of their javelins, were they named. They made a capture and a principality, for they were five brothers, the five sons of Dela f. Lot. And in a week they took Ireland, [though the days might have been different]. On the Saturday, August calendar, Slanga landed at Inber Slaine. On Tuesday Gann and Sengann boarded. On Friday Genann and Rudraige docked: and so it was a catch, although differently conceived. The Gaileoin, by Slanga were they named. By Gann and Sengann were named the Fir Bolg. The Fir Domnanns were named because they dug the earth: it was Genann and Rudraige and their retinue.
For they are all called Fir Bolg, and thirty-seven years was the duration of their authority over Ireland. The five sons of Dela were the five kings of Fir Bolg, namely, Gann, Genann, Rudraige, Sengann, Slaine.
§50. Slanga was the eldest, f. Dela f. Lot f. Oirthet, f. Tribe f. Gothorb f. Gosten f. Fortech f. Semeon f. Erglan f. Beoan f. Starn f. Nemed f. Agnomain. No king was said to be “of Ireland” until the Fir Bolg came.
Nine kings of these took Ireland. Slanga, a year - it was he of the Fir Bolg who died first in Ireland. Rudraige, two years, then he died at Brug Bratruad. Gann and Genann, four years, then they died of the plague at Fremaind. Sengann, five years, then he fell by the hand of Rindail f. Genann f. Of the. Rindail, six years, then he fell by the hand of Fodbgenid f. Sengann f. Dela to Eba Coirpre. Fodbgen, four years, then he fell to Mag Muirthemne by the hand of Eochu f. Rindail f. Genann f. Of the. Eochu son of Erc, ten years. There was no watering in his time, except dew only: there was no year without harvest. Lies were driven out of Ireland in his time. Through him was executed the law of justice in Ireland for the first time. Eochu son of Erc fell to the three sons of Nemed f. Badra: He was the first king of Ireland who received his fatal blow in Ireland.
§51. The Fir Bolg gave battle to Mag Tuired; great time lasted the combat in this battle. Finally it unraveled against the Fir Bolg, and the slaughter spread north, and a hundred thousand of their men were killed westward on the Eochaill shore. There was joined King Eochu, and it fell into the hands of the three sons of Nemed. However, the Tuatha De Danann suffered great loss in the battle, and they left the king on the battlefield, with his arm cut off; doctors spent seven years curing him. The Fir Bolg fell in battle all but a few, and they left Ireland fleeing the Tuatha Dé Danann, Ara, and Isle, and Rachra and other nearby islands. It was they who led the Fomoraig to the second battle of Mag Tuired. And they remained in these islands until the time of the Provincials over Ireland, when the Cruithne expelled them. They went to Cairbre Nia Fer, and he gave them land; but they were unable to stay with him because of the heavy tax he imposed on them. They subsequently fled from Cairbre under the protection of Medb and Ailill, and they gave them land. Such is the wandering of the sons of Umor. Oengus son of Umor was their king in the east, and after them are named these territories, Loch Cime de Cime Quatre-Têtes son of Umor, Pointe de Taman in Medraige de Taman son of Umor, the Fort from Oengus to Ara from Oengus, the rocks from Conall to Aidne from Conall, Mag Adair from Adar, Mag Asail from Asal to Mumu as well. Menn son of Umor was a poet. They were in the fortresses and sea islands around Ireland in this sense, until Cu Chulaind defeated them.
§52. These were the kings of the Fir Bolg and their dead;
So the poet says
The Fir Bolg were here a season
In the big island of the sons of Mil;
Of the five chiefs they brought with them
From there, I know their names.
One year had Slanga, it's true,
Before dying in his beautiful mound;
The first man of the Fir bolg of the peaks
Who died on the island of Ireland.
Two years of Rudraige the red,
Before I died in Brug Brat-ruaid,
Four of Genann and Gann,
Before the plague took them to Fremaind.
Five years of Sengann - they were restful -
Then Fiachu son of Starn killed him;
Five more - this was during a battle -
Fiachu Cendfhindan was king.
Fiachu Cendfhindan in front of all,
His name endures forever;
All fortunate, without reproach,
The children of Ireland were in his presence.
Then he fell by the hand of red Rindail,
He had six years with his free army;
Dela's grandson then fell to Eba,
By the hand of Odbgen.
Four to noble Odbgen until the battle
From Murthemne des nobles:
Odbgen died without reproach
By the hand of the son of Erc, of the great Eochu.
Ten years in Eochu son of Erc,
He did not find the border of weakness:
Then they killed him on the battlefield,
The three sons of Nemed son of Badra.
Then Rinnal grew up, there was no rush
On the Arms of Ireland;
On the rough javelins there was no thrusting,
They were just throwing sticks.
In Fodbgen's time thereafter
He came from the knots in the trees:
The woods of Ireland felled
Then they were smooth and very straight.
The pleasant Tuatha Dé Danann
Brought with them spears in their hands:
With them Eochu was killed,
By the descendants of Nemed in the strong judgment.
The names of the three excellent sons of Nemed
Were Cessarb, Luam, and Luachra:
It was they who killed the first king with a point,
Eochu son of Erc, in Ireland.
Subsequently the Tuatha Dé fought the Fir Bolg,
It was a successful appearance.
They took their property
And their governance to Men.
§53. Fintan says of the division of the Provinces -
The five parts of Ireland
Between sea and land,
I beg the beautiful candles
From every province among them.
From fast and fiery Drobais,
Is the first division up
The wide, white Boyne
South of the Blanche Bairche.
From the Boyne, harmonious and sparkling
With its hundreds of ports
At the crossroads to the sound of assembled waves
Of the three cold waters.
Of the same
Du Bel de Cu the brave
Which is called 'knell.'
From Lumnech to the imposing ships -
Large its surface -
To Drobais to the armed multitudes,
Pure, on which the sea laughs.
The related paths,
Perfection in correction
Towards a road in five.
The points of these provinces
In Uisnech they led,
Each out of his own […]
[…] Up to five.
Semeon's offspring were all Gaileoin and Fir Domnann. Thirty years after Genann and Rudraige, the Tuatha Dé Danann came to Ireland.
§54. Subsequently the offspring of Bethach f. Iarbonel the soothsayer f. Nemed was in the northern islands of the world, learning Druidism and lore and prophecy and magic, until he was expert in the arts of pagan cunning.