a few more SC shells I request help with

[paul monfils]

The larger bivalve is certainly Mercenaria mercenaria, the "Quahog". You are correct that the juvenile Mercenaria shells often have raised ridges on them which the adults do not have:

http://www.jaxshells.org/825a.htm?sa=X&v...s-Ch3zIQZP

However, the shells also have smoothly rounded anterior and posterior ends, just like the adults, as shown in this picture. Your specimen seems to be somewhat pointed at the end, which would suggest a Chione, so I think the "lady-in-waiting", Chione intapurpurea, would be a good guess.

The other shell is definitely a juvenile Busycotypus canaliculatus, "channeled whelk".