104 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 
animal food was less keen, and with the exception of a few cephalopods, a few large anne- 
lids, and a few Crustacea like Sidneyia, there seem to have been no aggressive carnivores. 
In consequence, millions of animals must have daily died a natural death, and had there been 
no way of disposing of their remains, the sea bottom would soon have become so foul that 
no life could have existed. For the work of removal of this decaying matter, the carniv- 
orous annelids and the Crustacea, mostly trilobites, were the only organisms, and it is prob- 
able that the latter did their full share. After prowling about and locating a carcass, the 
trilobite established himself over it, the cephalon and hypostoma on one end and the 
pygidium on the other enclosing and protecting the prey, which was shredded off and passed 
to the mouth at leisure by means of the spinose endobases. 
Even in Middle Cambrian times some trilobites (e. g., Parad oxides) seem to have en- 
larged the capacity of the stomach and taken vegetable matter, but later, in the Upper 
Cambrian and Ordovician, when the development of cephalopods and fishes caused great 
competition for all animal food, dead or alive, most trilobites seem to have become omniv- 
orous. This is of course shown by the swollen glabella, with reduced lateral furrows, and, 
in the case of a few species {Calymene, Ceraurus), the known enlargement of the stomach. 
Cryptolithus is the only trilobite which has furnished any actual evidence as to its food. 
From the fact that the alimentary tract is found stuffed from end to end with fine mud, 
and because it is known to have been a burrower, it has been suggested by several that it 
was a mud feeder, passing the mud through the digestive tract for the sake of what organic 
matter it contained. Spencer (1903, p. 491) has suggested a modification of this view: 
The phyllopods appear to feed by turning over whilst swimming and seizing with their more posterior 
appendages a little mud which swarms with infusoria, etc. This mud is then pushed along the ventral 
groove to the mouth. Casts of the intestine of trilobites are still found filled with the mud. 
Ceraurus and Calymene also must have occasionally swallowed mud in quantity, other- 
wise the form of the alimentary canal could not have been preserved as it is in a few of 
Doctor Walcott's specimens. 
TRACKS AND TRAILS OF TRILOBITES. 
Tracks and trails of various sorts have been ascribed by authors to trilobites since these 
problematic markings first began to attract attention, but as the appendages were until re- 
cently quite unknown, all the earlier references were purely speculative. The subject is a 
difficult one, and proof that any particular track or trail could have been made in only one 
way is not easily obtained. Since the appendages have actually been described, compara- 
tively little has been done, Walcott's work on Protichnites (1912 B, p. 275) being the most 
important. Since the first description of Protichnites by Owen (Quart. Jour. Geol. Soc, 
London, 1852, vol. 8, p. 247), it has been thought that these trails were made by crustaceans, 
and the only known contemporaneous crustaceans being trilobites, these animals were natu- 
rally suggested. Dawson (Canadian Nat. Geol., vol. 7, 1862, p. 276) ascribed them, with 
reserve, to Paradoxides, and Billings (1870, p. 484) suggested Dikelocephalus or Aglaspis. 
Walcott secured well preserved specimens which showed trifid tracks, and these were readily 
explained when he found the legs of Neolenus, which terminated with three large spines. 
Similar trifid terminations had already been described by Beecher, and clearly pictured in his 
restoration of Triarthrus, but the spines and the tracks had somehow not previously been 
connected in the mind of any observer. Walcott concluded that the tracks had been made 
