FEEDING. 
103 
chiefly in very fine-grained shales, in company with graptolites. These latter are distributed 
by currents over great distances within short periods. It is somewhat curious that the nearly 
blind burrowing Trinucleidae, the dysphotic, large-eyed Remopleuridse and Telephus, the blind 
nektonic Agnostidse and Dionide, and the planktonic graptolites should go together and make 
up almost the entire fauna of certain formations. Yet, when the life history of each type 
is studied, a logical explanation is readily at hand, for all have free-swimming larvae. 
A list of the methods of life noted above is given by way of summary, with examples. 
Pelagic 
Benthonic - 
Planktonic 
Nektonic 
Crawlers and 
slow swimmers 
Crawlers and 
active swimmers 
Crawlers, slow 
swimmers, and 
burrowers 
( Primarily 
( Secondarily 
'Primarily 
Secondarily 
Earliest protaspis of all trilobites 
Deiphon, Odontopleura, etc. 
Later protaspis of all trilobites. Naraoia 
' Probably many thin-shelled trilobites with large pygidia 
(only partially nektonic) 
Cyclopygids > (nektonic dysphotic) 
Remopleunda? \ 
Most trilobites with small pygidia. Triarthrus, Para- 
doxides, etc. 
Most trilobites with large pygidia. Isotelus, Dal- 
manites, etc. 
Trinucleidje, Harpedidse, some Mesonacidae, etc. 
FOOD AND FEEDING METHODS. 
This subject has been less discussed than the methods of locomotion. The study of 
the appendages has shown that while the mouth parts were not especially powerful, they were 
at least numerous, and sufficiently armed with spines to shred up such animal and vegetable 
substances as they were liable to encounter. It having been ascertained that the shape of the 
glabella and axial lobe furnishes an indication of the degree of development of the alimen- 
tary canal it is possible to infer something of the kind of food used by various trilobites. 
The narrow glabella; and axial lobes of the oldest trilobites would seem to indicate a 
carnivorous habit, while the swollen glabella; and wider lobes of later ones probably denote an 
adaptation to a mixed or even a vegetable diet. This can not be relied upon too strictly, 
of course, for the swollen glabella: of such genera as Deiphon or Spharexochus may be due 
merely to the shortening up of the cephalon. 
Walcott (191S, p. 125) suggests that the trilobites lived largely upon worms and con- 
ceives of them as working down into the mud and prowling around in it in search of such 
prey. While there can be no doubt that many trilobites had the power of burying them- 
selves in loose sand or mud, a common habit with modern crustaceans, most of them were 
of a very awkward shape for habitual burrowers, and how an annelid could be successfully 
pursued through such a medium by an animal of this sort is difficult to understand. In 
fact, the presence of the large hypostoma and the position of the mouth were the great 
handicaps of the trilobite as a procurer of live animal food, and coupled with the rela- 
tively slow means of locomotion, almost compel the conclusion that errant animals of any 
size were fairly safe from it. This restricts the range of animal food to small inactive 
creatures and the remains of such larger forms as died from natural causes. The modern 
Crustacea are effective scavengers, and it is probable that their early Palaeozoic ancestors 
were equally so. It is a common saying that in the present stressful stage of the world's 
history, very few wild animals die a natural death. In Cambrian times, competition for 
