A little research turns up that "Sharks exhibit a great diversity in reproductive modes. There are oviparous (egg-laying) species and viviparous (live-bearing) species."

Mermaid's purse: "This name is given to the egg cases of many sharks and skates. This tough, protective purse-shaped egg case contains one fertilized egg. A young shark or skate later emerges from the mermaid's purse. Shark species that utilize this mode of reproduction include the swell shark, dogfish, and angel sharks."

http://www.flmnh.ufl.edu/fish/education/questions/Biology.html#birth

The dogfish available through the Carolina Biological supply co are not specified, but I bet they are a viviparous species.