Sub-order 2. Eurypterida

"Crustacea with numerous, free, thoracico-abdominal segments, the first and second (?) of which bear one or more broad lamellar appendages upon their ventral surface, the remaining segments being devoid of appendages; anterior rings united into a carapace, bearing a pair of larval eyes (ocelli) near the centre, and a pair of large marginal or sub-central eyes: the mouth furnished with a broad post-oral plate, or metastoma, and five pairs of movable appendages, the posterior of which form great swimming-feet: the telson, or terminal segment, extremely variable in form; the in-tegment characteristically sculptured" (Henry Woodward).

The Eurypterida are all extinct, and are entirely confined to the Palaeozoic period. Many of them attained to a comparatively gigantic size; Pterygotus Anglicus (fig. 151) being supposed to have reached a length of probably six feet. In their characters they present many larval features; resembling the larvae of the Deca-poda especially in the fact that all the free somites of the abdomen (except the two anterior ones) were totally devoid of appendages.

Fig. 152.   Larva of Limulus on hatching, greatly enlarged. (After Dohrn.)

Fig. 152. - Larva of Limulus on hatching, greatly enlarged. (After Dohrn.)