214 BULLETIN OF THE 



other locality in the same condition of preservation. That most of 

 them are not the exuviated shell, resulting from the moulting, is 

 proven by the presence of more or less remains of the viscera and ap- 

 pendages associated with them, the viscera in the cephalic cavity 

 nearly always being present. Some are probably the cast shells ; but 

 the greater proportion of the larger specimens are those in which the 

 animal died. From observations made during several years collecting 

 in various formations it appears that the exuviated shell is usually 

 broken up. In some species, as the Calymene senaria at Cincinnati, 

 Ohio, many of the entire cast shells were undoubtedly buried in the 

 soft mud as soon as left by the animal, and tlius preserved entire. 



Manner of Life. — Burmeister gives us, as his view of the manner 

 of life the Trilobites led, '' that they most probably did not inhabit the 

 open sea, but the vicinity of coasts, in shallow water, and that they 

 here lived gregariously in vast numbers, chiefly of one species ; 

 that they moved only by swimming in an inverted position, and did 

 not creep about on the bottom ; that they lii'^ed on smaller water 

 animals, and, in the absence of such, on the spawn of allied species." 



Barrande supposed that they lived in deep water and swam on the 

 surface of the sea. 



Dr. Dohrn considers that they lived at the bottom of the sea, and 

 with extremities like those of Limulus crawled about. This view was 

 necessarily taken by all authors who considered the Trilobite as 

 related by its zoological affinities to Limulus. From our present 

 knowledge of its structure, we cannot but suppose that its habits and 

 manner of living were similar to the living Arthropods to which it is 

 most closely allied. That its natator}^ powers were slight there is 

 evidence in the absence of swimming appendages that could have been 

 of much service to the adult individual. In the j-ounger stages of 

 growth these were probably of great size as compared with tlie other 

 appendages, and used for swimming. From the great geographical 

 distribution of many species it is evident that its means of locomotion 

 were greater during some period of its existence than when full 

 grown, as, from its massive structure then, it must have been limited 

 in its range and means of distribution. 



Dr. Packard states* that Mr. Alexander Agassiz had captured the 

 larva of lAmulus swimming free on tlie surface of the ocean, three 

 miles from the shore. From the comparisons made by Dr. Packard 



• DeFelopment Limulus polyphemus. Memoirs Boston Soc. Nat. Hist., p. 155, 

 1872. 



