72 NEW YORK STATE MUSEUM 
blatt fungiert haben und die mehr oder weniger vertikale Stellung des- 
selben beim Schwimmen durch die Gelenkverbindungen der wbrigen 
Gheder, besonders diejenigen zwischen dem fiinften und sechsten Gliede 
stattgefunden haben. Das bedeutende Zurtickbiegungsvermégen des acht- 
en Gliedes hat gewiss zur Verminderung des Widerstandes des Wassers 
bei der Zurtckfuhrung des Ruderfusses, um einen neuen Schwimmangriff 
machen zu konnen, gedient. Hiermit hangt 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 Platyonichus oculosus [focellatus], 
welcher in seinem Baue eine grosse und interessante Aehnlichkeit mit 
dem Ruderfusse von einem Furypterus 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 ex- 
pression with the supposedly analogous structural features of the euryp- 
terids. 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. 8. 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 for- 
wards, 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 1s 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. Lioyd on living Limuli in the aquarium at Hamburg. 
At Hamburg, specimens of Limul: were kept alive from the year 1865 
to 1870. From his observations of these Mr Lloyd informs me, “'the ulterior 
