The bi-ramose structure of the post-oral limbs, demonstrated by Beecher in the trilobite Triarthrus, is no more inconsistent with its claim to be a primitive Arachnid than is the foliaceous modification of the limbs in Phyllopods inconsistent with their relationship to the Arthrostracous Crustaceans such as Gammarus and Oniscus.
(b) Pedibus 8-14; capite thoraceque unitis: Acarus, Phalangium, Aranea, Scorpio, Cancer, Monoculus, Oniscus.
C. Fabricius instituted the genus Gammarus for five species, of which only three were amphipods, while he left five other amphipods in the genus Oniscus, from this total of eight science has developed the order, at first very slowly, but of late by great leaps and bounds, so that now the Gammaridea alone comprise more than 1300 species, distributed among some 300 genera and 39 families.
Nebalia, Astacus, Oniscus, Gammarus.
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