organisms, than the belief, which I hold, that Palaeophonus lived in the sea, probably in shallow water, its strong sharply pointed legs being admirably fitted, like those of a crab, for maintaining a secure hold amongst the seaweed or on the jagged surface of rocks, and for resisting the force of the rising and falling waves."
We have seen above that Fritsch believed there were indications of lung sacs in Proscorpius osborni, but inspection of the specimen has failed to reveal any traces of respiratory organs.
Although the discussions of the authors cited demonstrate that the ventral side of the mesosoma is not shown well enough in any of the four Siluric scorpions to settle the question of the presence or absence of stigmata or the life habit of these scorpions, we feel that Whitfield's, Laurie's and Pocock's suggestion of their probable aquatic habitat is well worthy of serious consideration. It is therefore pertinent to summarize here the arguments in favor of this view.
1 All four scorpions have been found in marine beds and in such good preservation that it is difficult to assume they drifted out to sea; especially since the beds containing them do not afford any other remains of land animals or plants. On the other hand, we should note in this connection that they all four occur in association with eurypterids, and these are considered in this publication as having been principally inhabitants of estuaries. But this association may, as indicated under 3, have rather a phylogenetic than a physical cause.
2 If the Siluric scorpions agree with the recent ones in respect to the body form and arrangement of the prosomatic appendages, then it does not follow, as pointed out by Laurie [loc. cit. p. 577], that they have reached the same point of specialization in respect to their respiratory organs. "The terrestrial mode of life and consequent adaptation to airbreathing may have come later."
3 As Pocock has shown that the arrangement of the parts constituting the ventral side of the prosoma in Palaeophonus indicates that the latter "occupies an intermediate position between Limulus and the
