Shell Drawing

I struggled a bit with this drawing.

With this assignment we were supposed to take our shell and follow its cross contours across the page, making the shell as large as possible on the page along the long axis.  I feel that everything was positioned appropriately, although I could have had a higher view of the shell as it looks a bit like I was drawing the shell head on.  Obvious things to improve on would be varying line weight and position.  Everything is webbed with roughly similar lines.  There is some variation, with the best parts of the drawing representing this in the first row of outward spurs.  i couldn't seem to get any of the same feel of form in the upper half of the shell, which was done in a separate sitting than the first half of the shell.  There is a bit of fading in the upper half which is successful in that it was the further side.  This was intentional, but could have been more dramatic.  I outlined the shell, not with a simple outline but with various cross contours that come together to make up one outline.  In a future drawing I would like to try to break up the outline and create some implied line.  In addition I want to do the entire drawing in one sitting to avoid the disjointed pieces I have in this drawing: the bottom half being feeling full and alive with the top half feeling flat and dull.  All in all I think I learned from the experience and will be able to take what I learned and apply it to my next drawing.