Check out this link,
http://nefsc.noaa.gov/sos/spsyn/species.html
It has illustrations and text on some of the fish found in the the Northeast, including the spiny dogfish. should help you ID it.
http://nefsc.noaa.gov/sos/spsyn/species.html
It has illustrations and text on some of the fish found in the the Northeast, including the spiny dogfish. should help you ID it.