So i haven't finished the story for romulan yet but why do I get the feeling the Elachi are the same race as the one from Next Gen that abducted members of the Enterprise D and experimented on them. The episode was called Schisms.
Although, Memory Alpha says that it is implied that they are the same race. To me, the aliens in ST: Enterprise, episode 'Silent Enemy' looked more like the Elachi.
They're definitely the aliens from Silent Enemy. The Elachi's Escorts are similar in design to the alien's ship (the Frigates might be a closer match, but I've never taken the time to look at one closely under cloak), and the aliens themselves have the same appearance. That, and they were hinted at in the LoR reveal as the "Silent Enemy."
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http://images2.wikia.nocookie.net/__cb20120511073602/memoryalpha/en/images/b/ba/Solanogen-based_lifeform.jpg
Although, Memory Alpha says that it is implied that they are the same race. To me, the aliens in ST: Enterprise, episode 'Silent Enemy' looked more like the Elachi.