Page:The Eurypterida of New York Volume 1.pdf/74

 fungiert haben und die mehr oder weniger vertikale Stellung desselben beim Schwimmen durch die Gelenkverbindungen der übrigen Glieder, besonders diejenigen zwischen dem fünften und sechsten Gliede stattgefunden haben. Das bedeutende Zurückbiegungsvermögen des achten Gliedes hat gewiss zur Verminderung des Widerstandes des Wassers bei der Zuruckführung des Ruderfusses, um einen neuen Schwimmangriff machen zu können, gedient. Hiermit hängt auch die, wie wir schon oben gesehen haben, scharfe, schneideartige Form des Vorderrandes des vierten bis sechsten Gliedes zusammen. Hall hat einen Schwimmfuss eines jetzt lebenden Krustenthieres  [ocellatus], welcher in seinem Baue eine grosse und interessante Aehnlichkeit mit dem Ruderfusse von einem Eurypterus zeigt, abgebildet. [1898, p. 27]

We have to gather our evidence by analogy from the habits of the living relatives of the eurypterids and of similarly built marine animals, comparing the structures in which their habit finds its most distinct expression with the supposedly analogous structural features of the eurypterids. With a view to this end, we may briefly consider the habits of Limulus, the common king crab, and those of crabs with swimming legs as in the eurypterids.

An early and excellent account of the habits of the king crab was given by the Rev. S. Lockwood (cited by Owen [1872]) who says:

It is emphatically a burrowing animal, living literally in the mud, into which it scoops or gouges its way with great facility by means of the anterior edge of its enormous cephalic shield. In the burrowing operation the forward edge of the anterior shield is pressed downwards and shoved forwards, the two shields being inflected, and the sharp point of the tail providing the fulcrum as it pierces the mud, while underneath the feet are incessantly active, scratching up and pushing out the earth on both sides. There is a singular economy of force in this excavating action, for the alternating doubling up or inflecting and straightening out of the two carapaces with the pushing purchase exerted by the tail spine, accomplish both digging and a subterranean progression. Hence the king crab is worthy to be called the "marine mole."

As to the use of the last pair of legs in burrowing and the use of the tail spine in locomotion, Owen also cites the interesting observations of W. A. Lloyd on living Limuli in the aquarium at Hamburg.

At Hamburg, specimens of Limuli were kept alive from the year 1865 to 1870. From his observations of these Mr Lloyd informs me, "the ulterior}}