I woke up this morning feeling as if I had received a bit of "divine revelation" on how to look for him. Previously, I had no luck in searching for him at the Ancestry.com database for the 1870 census by name, or even a line by line browsing of the township where I thought he should be. This morning I tried a different tack.
Focusing on his wife, Mary, I entered information in the search parameters only for her name, date of birth within 2 years, state of birth and then the presumed locality of Darke County, Ohio. There was only one result found for the 1870 census that matched my parameters.
When I clicked on the image, I had found my family :
Source: Luman Lemasters household, 1870 census, Allen Twp., Darke County, Ohio, dwelling 79, family 79, Ancestry.com [database on-line]
The handwriting is not good, and I can see why it was transcribed as Pemantus instead of Lemasters. Also, for some reason, the image is indexed as Brown Township, Darke County, Ohio when it is clearly Allen Township. I submitted an indexing correction to Ancestry.com so that others will be able to find the image in the future.
Luman Lemasters was a 27 year old farmer, born in Ohio, with real estate valued at $1000 and personal property valued at $700 and a U.S. citizen. His wife, Mary, was aged 23, born in New Jersey and keeping house. Daughter Eula (Beulah) was aged 5, born in Indiana, and son Luman was aged 3, also born in Indiana. With their daughter listed as Eula it was no wonder I couldn't find her when I searched for "Beulah" before.
I thought I had tried all the possibilities, but for some reason I hadn't found them. In this case, it was good that I listened to my intuition.