Ugh....

[Paciphacops]

I would suggest you fill the cracks on the back with Apoxie sculpt, in order to practice getting a good color match and texture. That will give it plenty of strength and once the back is finished, you should be ready to tackle the front. 

[Bone guy]

Here is the finished result! (Well, almost finished. I still have to clean up some spots of glue with acetone oops) I glued the cracks on the back side for extra support, but I certainly will get some epoxy sculpt in the future. But for now it's secure. I'm not happy that it broke, but I looked at this as an opportunity to prep a heliobatis radians!  Thank you @Ptychodus04, @sseth, and everybody else for all the advice and input throughout this journey! 

 

I'll post better pics of the specimen in my chondrichthyes album

 

[Kane]

Well done! A displayable piece... With character!  You made the most of a difficult situation. Bravo!

[Ptychodus04]

Well done @Bone guy. Repairing broken fossils is a huge part of preparation. This looks really good.