The kinds of sediments in which trilobites are entombed have so far afforded little evidence as to their habitat. Frech (Lethæa palæozoica, 1897-1902, p. 67 _et seq._) who has collected such evidence as is available on this subject, places as deeper water Ordovician deposits the "Trinucleus-Schiefer" of the upper Ordovician of northern Europe and Bohemia, the "Triarthrus-Schiefer" of America, the "Asaphus-Schiefer" of Scandinavia, Bohemia, Portugal, and France, and the Dalmania quartzite of Bohemia. . _Cryptolithus_ and _Triarthrus_, although not confined to such deposits, are apt to occur 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 Trinucleidæ, the dysphotic, large-eyed Remopleuridæ and Telephus, the blind nektonic Agnostidæ 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 larvæ. A list of the methods of life noted above is given by way of summary, with examples. {Planktonic {Primarily Earliest protaspis of all trilobites { {Secondarily _Deiphon_, _Odontopleura_, etc. { Pelagic { {Primarily Later protaspis of all trilobites. { { _Naraoia_ { { { { {Probably many thin-shelled { { { trilobites with large pygidia { { { (only partially nektonic) {Nektonic {Secondarily {Cyclopygidæ } {Remopleuridæ } (nektonic dysphotic) {Crawlers and { slow swimmers Most trilobites with small pygidia. { _Triarthrus_, _Paradoxides_, etc. Benthonic {Crawlers and Most trilobites with large pygidia. { active swimmers _Isotelus_, _Dalmanites_, etc. { {Crawlers, slow { swimmers, and Trinucleidæ, Harpedidæ, { burrowers some Mesonacidæ, 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 alimentary canal it is possible to infer something of the kind of food used by various trilobites.