. . ustacea. The first trunk limbs have already been mentionedas large rowing limbs. It was in one sense naturalthat the powerful limb should also develop a powerfulventral parapodium functional as a jaw, but the unionof the two functions is not easily comprehensible, andwe are more than ever inclined to think that the twomay have been separately articulated with the body. The limbs of Eurypterus differ markedly from thoseof Pterygotus. In front of the large rowing limb, first trunk limb, we have only four limbs visible inthe
. . ustacea. The first trunk limbs have already been mentionedas large rowing limbs. It was in one sense naturalthat the powerful limb should also develop a powerfulventral parapodium functional as a jaw, but the unionof the two functions is not easily comprehensible, andwe are more than ever inclined to think that the twomay have been separately articulated with the body. The limbs of Eurypterus differ markedly from thoseof Pterygotus. In front of the large rowing limb, first trunk limb, we have only four limbs visible inthe figure, all of these appearing to be sensory, andthus affording a striking contrast to the head limbs ofPterygotus, none of which appear, at first sight, to be SECT. XIV THE EURYPTERID^E 245 sensory. From our point of view, according to whichthe larirc rowing limbs belong to the first trunk seer- o o o o mcnt, we should have had to conclude that one pair oflimbs had disappeared. Such a supposition is howevernot necessary, as F. Schmidt has found and described. pIG- 56.—Eurypterus Fischer! Eichw. : Upper Silurian, natural size, after (from ZitteLs Handbnch der Palceontologie). Between the first pair of feet,Schmidt found a fine pair of feelers, corresponding with the Antennules of theother Crustacea. a pair of rudimentary antennae between the first pair,so that Eurypterus possesses the typical number ofhead appendages. It is a fact generally accepted thatthe pair of large rowing limbs corresponds with thatof the sixth segment. There is, however, no generalagreement as to whether these first six segments form 246 THE APODIDyE PART n a head or a cephalothorax. Our homology of the largelimb with the first trunk limb, throughout all theseprimitive Crustacea, shows that the six segments ofthe Eurypteridae form a cephalothorax, and not onlya head. This degeneration of the anterior antennae inEurypterus is hardly what we should have expectedtheoretically. The rapid forward
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