I have just discovered that there is a group of Gypsies called Sinti (or Sinto) that is apparently distinct from the Roma, but I am unable to find detailed information other than that they mostly hail from northern and western Europe (Germany, France, the Netherlands, &c.). It seems to be politically correct in Germany to speak of “Sinti and Roma” rather than “Zigeuner” (Gypsies). If anyone out there knows more (for example, whether there are linguistic differences), I would be much obliged if you’d pass it on. It’s very hard on me when both the internet and my excessively laden bookshelves fail me.
Addendum. And that goes for the Jenisch (or Yenish or Yeniche) too.
Answer. The learned Bob Cohen has provided the following information in the comments section, which pretty much clears the matter up; thanks, Bob!
Speaking of “Roma and Sinti” is like saying “Jews and Sephardim”. The Sinti dialect is definately Rromanes, but not intelligible to speakers of Kalderash or Balkan Rromanes. They mix in a lot of German influence and lack the heavily Romanian influences of Kalderash/Vlashiko…. As for Jenische, it isn’t very much spoken any more—there is a Jenische web page for Swiss Jenische, they seem to have been a non-Rroma group who adapted and intermarried with Rroma.