. The Canadian journal of industry, science and art. A REVIEW OE THE TRILOBITES. 281 The trilobites appear at the base of the Silurian formations, and die out in the lower Carbonifeixms. They constitute the only order of crustaceans of which we have no living representatives. The phyllopods appear also at the base of the Silurians. The lo- phyropods (cyprids, &c.) follow the same law. The cirrhopods com- mence their existence with the lias—at least, if the doubtful bostri- chopus be excluded from the group. Of the siphonostoma, no fossil representatives are known. These geological relation
. The Canadian journal of industry, science and art. A REVIEW OE THE TRILOBITES. 281 The trilobites appear at the base of the Silurian formations, and die out in the lower Carbonifeixms. They constitute the only order of crustaceans of which we have no living representatives. The phyllopods appear also at the base of the Silurians. The lo- phyropods (cyprids, &c.) follow the same law. The cirrhopods com- mence their existence with the lias—at least, if the doubtful bostri- chopus be excluded from the group. Of the siphonostoma, no fossil representatives are known. These geological relations are presented at a single view in the accompanying scheme:—*. 7. Classification. The arrangement of the trilobites in natural groups is beset with considerable difficulty. This arises in part from e fragmentary condition in which so many species are commonly met with ; and partly from our still imperfect knowledge of the true value of the various organization characters on which we are obliged to base our collocations. Owing to the first source of error, it has often happened that distinct types have been formed into a single species ; whilst on the other hand, imperfect specimens of one and the same species have been referred to even different genera. A sys- * All the fossiliferous rocks below the Devonian group are ban included in the term Silu- rian. The Lotihyrojioda should he drawn down t the Lovwi hoi izontft] Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Canadian Institute. Toronto : Canadian Institute
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