The hours of work spent trying to get the decrement to simulate properly allowed me to finish all of the pieces of Turtle's upper shell!
I'm not sure how well it shows up in the picture, but the "squares" are actually rectangles: 16 stitches wide by 22 rows tall. The triangles are 20 stitches wide at the base by 20 rows tall. The tall side of the rectangle actually will match fairly closely with the sides of the triangle. However, I'm still stumped on how to sew the short side of the rectangles to the triangle. I may knit up a few extra pieces to practice on, because I think this finishing job will involve stretching the pieces and in my experience that doesn't look good after ripping. The pieces are nice and small (they fit great in the really limited space on my computer desk) and are quick to knit - even for me. (And I think this is why I haven't restarted the section of Catherine that I ripped out. Catherine is worsted weight yarn on size 3's, as is Turtle. However, the current piece that I'm working on for her is approximately 50 stitches wide by 100 stitches tall, so it is a much longer piece of knitting and my attention span are free time are both perilously small recently.
And just on an off tangent, why the flip are computer books so expensive. I picked up some books that will help me with work and spend $118 on three books. (I prefer to pay for them myself as that way they are actually my books.)