Complex sentence: There are fifteen species belonging to the genus "Eurypterus", the most common of which is "Eurypterus remipes", the first eurypterid fossil discovered and the state fossil of New York.
Split into simpler sentences: There are fifteen species belonging to the genus "Eurypterus". The most common of which is "Eurypterus remipes", the first ever discovered eurypterid fossil and the state fossil of New York.