378 



THE OSTRACODERMS. 



zontal plane. They had either fallen to the bottom in this position when ex- 

 hausted, or turned over in the death struggle, so that the trunk and fins laid 

 flatwise on the upper surface of the muddy bottom. One specimen was found 

 standing on its head, almost vertically. It had evidently been swimming at some 

 speed, when taking a sudden turn, it struck the soft bottom, head first, with suffi- 

 cient force to stick there in an upright position. This individual was not in the 



FIG. 257. Photographs of three contiguous slabs, from approximately the same level, and with the same 

 orientation. The slabs are seen from their under surfaces, and show the uniformity in the orientation of the numer- 

 ous specimens of Bothriolepis. All are in a natural position, and are headed in the same direction, except four. 

 Of these, two have the ocular, or neural surface exposed (i.e., they lie, haemal side up, when the slab is in its original 

 position) ; one lies on its side; and one, a, lies with its head toward the reader; its tail is gracefully curved toward 

 the upper right-hand corner, apparently by a gentle current of water, that turned the tops of the enclosed water 

 plants in the same direction. 



least flattened in a dorso-ventral direction, and when sectioned showed the re- 

 mains of the viscera settled down in the lower or anterior end of the head. In 

 all other cases the viscera were found lying either on the dorsal or on the ventral 

 wall of the branchiocephalon, according to the side that happened to be upper- 

 most when the animal died. 



