Below are four different genera who's names are often used interchangeably by some dealers and collectors who have not yet learned the differences.
This is how I tell the different genera apart in the field and in my collection.
The easiest to separate out is
The next commonly confused shell is that of Paraspirifer. Paraspirifer has a large, walnut shape and a very deep sulcus in the middle of the shell. when you turn the specimen around you'll notice that the Brachial and Pedicle valve curve in towards each other and nearly touch.
In the middle between Paraspirifer and Spinocyrtina is
Lastly we have Platyrachella which has a similar body plan and shape to Mediospirifer, but Platyrachella's hinge line is wider than Mediospirifer's and it's interarea has a more pronounced curve.
Hopefully this makes sense and I'm not too far off on my logic. There are many other species that have similar looks to the above four examples but I'm not going to get into that much detail. Have a different opinion? Let me know in the comments.