THE ANTIARCHA. 



379 



In the large slabs containing many ferns or plant stems, it was clearly shown 

 that the plants were laid down in nearly parallel lines with the tops turned in the 

 same direction, as though at the time they were deposited they had been bent 

 over by a slow current of water. 



One of the larger slabs, containing ferns and Bothriolepis in great numbers, 

 is specially instructive. (Fig. 257.) It shows most of the fern tops turned in one 

 direction, with most of the Bothriolepis heads turned in nearly the opposite 

 one, their thin, soft bodies extending in straight lines backward. But one speci- 

 men, A, is lying on its back in a direction diagonal to the fern tops, thus show- 

 ing that when this individual died it fell on the bottom oral side up; that the 

 current then turned it partly around, bending its tail in a gentle curve in the 

 same direction as the fern tops. 



In some cases several individuals of Bothriolepis were found close together, 

 and at different levels, but nevertheless all turned in the same direction, showing 

 that they were probably oriented by the same agents and died at the same time. 

 From these facts we may infer that they were moving along the soft bottom, 

 some completely covered with mud or sand, others on the surface, just as the 

 adult Limuli do when in great swarms they come up the sandy beaches at high 

 tide to lay their eggs; or as the young Limuli, when feeding, plough about 

 through the soft mud, from three to six inches below the surface. 



Locomotion. It is evident, therefore, that Bothriolepis was a bottom feeder, 

 moving about on its flat oral side, either covered by soft sand or mud, or leaving only 

 its projecting eyes and dorsal surface exposed. But it is evident that it was also 

 a free swimming form, using both its flexible tail and trunk and its large cephalic 

 appendages for that purpose. They probably swam, with their flat oral side up- 

 permost, by powerful backward strokes of their cephalic appendages, just as the 

 eurypterids and possibly many trilobites did in the palaeozoic seas, and as many 

 phyllopods, entomostrica, or indeed as adult Limuli continue to do to-day. 



It will be observed that the appendages are attached well forward on the 

 margin of the flat and narrow ventral surface; that the head is quite thick, and 

 the dorsal surface wide and strongly arched. A body shaped like this would 

 naturally move through the water like a boat right side up. It is evident that 

 Bothriolepis could not be driven through the water, dorsal side up, without a 

 strong tendency to pitch downward head first, or to roll over. As the cephalic 

 appendages were very narrow and had little dorso-ventral movement, they could 

 hardly succeed in counteracting, or preventing, that tendency. Hence it is clear 

 that the animal had to swim with its dorsal side down, and with its center of 

 gravity below the level of the supporting appendages. In this position equilib- 

 rium could easily be maintained either by the arms or by the tail, and the curved 

 anterior surface of the head, according to the rate of its forward movement, would 

 greatly aid in uplifting the cumbersome head in the water. 



Food. Well preserved specimens always contain, in addition to the rem- 

 nants of other soft parts, a thick oval disc of carbonaceous material, that undoubt- 



