Because all three of the G.B Sowerbys published extensively on the subject of conchology , it is not easy even for professional taxonomists to unravel which of the three `` G.B. Sowerbys '' is meant in a particular citation when the numbering system G.B. Sowerby I , II , or III is not used .
Even for professional taxonomists it is difficult to know which of the three `` G.B. Sowerbys '' is meant in a particular citation .