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 thus 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 lived 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 zoülogical 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 natatory 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 younger stages of 
growth these were probably of great size as compared with the 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 Limulus swimming free on the surface of the ocean, three 
miles from the shore. From the comparisons made by Dr. Packard 
* Development Limulus polyphemus, Memoirs Boston Soc. Nat. Hist., p. 155, 
1872. 
