they are different species..... the maxima grow larger, faster and are found at greater depths than the crocea. they also have several physical differences, like shell shape, scute spacing, mantle shape / pattern, byssal and exhalent syphon openings.
the requirements for the two are basically the same with the crocea being slightly hardier but requirer a little more light, though the maxima will greatly appreciate the extra light too.
HTH