A "fresher" picture as well

What kind of grass do you have that is thinning out?
What is your watering schedule (frequency and amount)?
How high/low do you mow?
How often do you fertilize and what do you use?

Bermuda. Water every 2-5 days when green depending on temperature, 1/2" a watering. Haven't watered since Oct. Mow 3.5". Mowed a little shorter, 2.5", after it went dormant. Fertilize on a schedule from local John Deer Landscapes....Mar, May, Jun, Jul, Sep. Exact mix varies.

Grant, what you have -- your "casings" -- are rhizomes of the common blue violet, Viola sororia (or a relative), and a few rather unhappy leaves.

In my lawn, these violets grow in shady areas where the grass can't compete. (My grass in a sort of Heinz 57 varieties -- and if you have shady places, I'm sure your Bermuda isn't happy there.)

http://purdueturftips.blogspot.com/2013/06/mays-weed-of-month-wild-violets.html

http://www.greengrassok.com/Your-Lawn/weeds---weed-control/wild-violets/

Thanks for the answers. Shade is likely to be your problem leading to thinning.

In addition to shade, you are watering far too frequently and mowing too high. Search for the Bermuda Bible online and memorize it.