Contour Shell Drawings

I did two contour line drawings of the shell one on the left is the second one I did and the one on the right is the first one. I found drawing contour lines of a shell was very difficult compared to the knee contour drawing I had done last week. I felt that I couldn't get the directions of the contour lines I wanted and got very frustrated quickly. I also tried working with hard and soft lines but I am not sure how happy I am with them. In each drawing of the shells I did enjoy a few parts of the drawings; the one on the right I liked the very front of the shell. I know one of my problems is that I am a fast pace person and it is hard for me to slow down. I also have a tendency to redraw lines over and over until I get them correct. What I do need to practice on is getting into the mode of slowing down more so that I can analysis my subject better.