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"The first three pairs of mesosomatic appendages of Scorpio and Limulus compared. VII. The genital operculum; VIII. The pectens of Scorpio and the first branchial plate of Limulus; IX. The first pair of lung-books of Scorpio and the second branchial plate of Limulus. gp, Genital pore; epst, Epistigmatic sclerite; stg, Stigma or orifice of the hollow tendons of the branchial plates of Limulus." — The Encyclopedia Britannica, 1910

Mesosomatic

"The first three pairs of mesosomatic appendages of Scorpio and Limulus compared. VII. The genital operculum;…