Criteria for species, phylogenies, and faunas of trilobites
Introduction The describer of trilobites has an advantage over the student of Brachiopoda, Mollusca, and various other invertebrates in that the animals with which he deals have more parts, and hence present more combinations of characteristics which may be used in the discrimination of species. On the other hand, he suffers from the disadvantage that his specimens are apt to be dismembered, and very many species are known from fragments only. Due, perhaps, to this latter contingency, trilobitists have, as a rule, been rather conservative, and it is only within the last few years that an era of nice distinctions has been inaugurated. Compared with the number of individual specimens, the number of species and genera of trilobites still remains few, but bids fair to be increased rapidly in the next decade or two. Characteristics of the Body The body of the trilobite is doubly tripartite, but the longitudinal division . . .