When I searched "McLauchlin family" in the LOC catalog, I got no results on that spelling.  However, searching "McLaughlin family" turned up 17 items.  These are the ones I plan to investigate (1st stop is to check if these are available at Clayton here in Houston):

1 -- A memorial history of the Campbells or Melfort, Argyllshire. published in London: Simmons & Botten, 1882. From my research, I have learned that at least one branch of the McLauchlins were part of the Campbell clan, so this may prove fruitful, if only for background.

2 -- McLaughlin-McGonegle / McGonigle: the four Irish immigrants: their origins, history, and descendants by Anita Helen Dolan, published in Des Moines, Iowa: A. H. Dolan, 1981. The more I research, the more I have come to believe that the spelling of our surname with a "g" is the Irish spelling. My paternal grandmother, Lula Mylinda Sullivan, was Irish. Perhaps she taught my dad to spell his last name the Irish way; just a theory, but no way to prove it now. Still, it might be worthwhile to learn more about the McLaughlins of Ireland. JennieV was never able to trace our immigrant ancestor, Dugal, to a specific locale in Scotland. Perhaps he made a detour through Ireland, or Jamaica (a common first port for Scots emigrants of that time).

3 -- Memorial history of the family of Campbell-Maclachlan by Archibald Neil Campbell, 1819-1891, published in London: S. Goldbourn, 1883. This seems a more promising lead. If there is no mention of Dugal, then it will make good background information on his branch.

4 -- The McLaughlin family history by Arthur Lee McLaughlin. Owensboro, KY: McDowell Publications, 1980. A history of the family in the U.S.

5 -- A history of the very early colonials -- The McLaughlins by Gerald William McLaughlin. Albuquerque, N.M.: G. W. McLaughlin. 1995. After JennieV's research, this may have something of value...worth checking at any rate.

6 -- The McLaughlins by Steven K. McLaughlin & Evelyn Z. McCann. Dallas, TX: S.K. McLaughlin. 1988. Published the same year that JennieV published The McLauchlins: Fortis et Fidus, and not far from JennieV, I wonder if there is a connection? Certainly worth checking.

7 -- The McLaughlin genealogy: descendants of James and Mary McLaughlin of Muff (now Eglinton), County Londonderry, Ireland: related families, Brown, Johnston, Lossee, Morford, Parker, Speir, Woods by Steven K. McLaughlin. Dallas, TX: S.K. McLaughlin, 1990. A second title published in Dallas. 

I searched all seven of these in the Houston Public Library (Clayton) catalog.  It has none of these in its collections. So, I will have to wait until my next visit to the LOC to investigate these books.
I think I feel a trip coming on.