  The primary object of this memoir is, as has been stated by Professor Schuchert, to. rescue from oblivion the results of the last few years of Professor Beecher's investigations on the ventral anatomy of trilobites. Since he left his data in the form of drawings and photographs, without even rough notes, it became necessary, in order to write a text to accompany the plates, to restudy the entire subject. Under these circumstances, it seemed best to include all that is known about the appendages of trilobites, thus bringing together a summary of present information on the subject. The growth of the memoir to its present size has been a gradual one. As first completed in 1917, it contained an account of the appendages only. Thoughts upon the probable use of the appendages led to the discussion of possible habits, and that in turn to a consideration of all that is known or could be inferred of the structure and anatomy of the trilobite. Then followed an inquiry into the relationships to other Arthropoda, which ultimately upset firmly established preconceptions of the isolated position of the group, and led to a modification of Bernard's view of its ancestry. During the progress of the work, I have had the opportunity of examining most of the known specimens retaining appendages. From the Marsh collection in the Yale University Museum were selected the forty-six specimens showing best the appendages of Triarthrus, Cryptolithus, and Acidaspis. Dr. Charles D. Walcott very kindly returned to the Museum of Comparative Zoology the slices of Ceraurus, Calymene, and Isotelus which were the basis of his paper of 1881, and which had been loaned him for further study. He loaned also eight of the more important specimens of Neolenus serratus, and two of Triarthrus becki. At the United States National Museum I saw the specimens of Isotelus described by Mickleborough and the isolated limbs of Calymene from near Cincinnati. The Isotelus at Ottawa I had already studied with some care while an officer of the Geological Survey of Canada. This memoir consists, as shown in the table of contents, of four parts. The appendages of Neolenus, Isotelus, Ptychoparia, Kootenia, Ceraurus, Calymene, and Acidaspis are discussed, as fully as circumstances warrant, in the first part, and new restorations of the ventral surfaces of Neolenus, Isotelus, Triarthrus, Ceraurus and Cryptolithus are included It is not supposed that these restorations will be of permanent value in all of their detail, but they are put forward as the best approximations to the real structure that the writer is able to present from the materials so far discovered. I am greatly indebted to Doctor Elvira Wood for the care and skill with which she has worked up these restorations from my rather sketchy suggestions. She has put into them not only a great amount of patient work, but also the results of considerable study of the specimens. Part II is a discussion of the internal anatomy of the trilobite and a brief statement of some of the possible habits and methods of life of these animals. Part III, which begins with a survey of the relationships of the trilobites to other Arthropoda, is largely taken up with an attempt to demonstrate the primitive characteristics of the former, and their probable ancestral position. The form of the ancestor of the trilobite is deduced from a study of the morphology, ontogeny, and phylogeny of the group, and evidence adduced to indicate that it was a depressed, flattened, free-swimming animal of few segments. In Part IV are included somewhat detailed descriptions of a few of the best specimens of Triarthrus and Cryptolithus. Professor Beecher, while an observer of the minutest details, believed in publishing only the broader, more general results of his investigations. This method made his papers brief, readable, and striking, but it also resulted in leaving in some minds a certain amount of doubt about the correctness of the observations. In a matter so important as this, it has seemed that palÆontologists are entitled to the fullest possible knowledge of the specimens on which the conclusions are based. The last part is, therefore, a record of the data for the restorations of Triarthrus and Cryptolithus. The illustrations in the plates were nearly all made by or under the supervision of Professor Beecher, as were also text figures 45 and 46. In conclusion, I wish to express my thanks to Mrs. Charles E. Beecher for the use of drawings which were the personal property of Professor Beecher; to Doctor Charles D. Walcott for photographs of the limbs of Calymene, and for his kindness in sending me the slices of trilobites from Trenton Falls and specimens of Neolenus and Triarthrus; to Doctor R. V. Chamberlin for suggestions and criticisms in regard to the relationship of trilobites to Insecta, Arachnida, Chilopoda, and Diplopoda; to Mr. Samuel Henshaw, Director of the Museum of Comparative Zoology, for permission to use the time which has been devoted to this work; and to Miss Clara M. Le Vene, for assistance in the preparation of the manuscript. My greatest debt is to Professor Charles Schuchert, to whom the work owed its inception, who has assisted in many ways during its prosecution, and who read the manuscript, and arranged for its publication. To him I can only express my warmest thanks for the favors which I have received and for the efforts which he has put forth to make this a worthy memorial to our friend and my teacher, Professor Charles Emerson Beecher. Harvard University, Cambridge, Mass. |
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