PREFACE vii 



fisheries, and Dr. Arthur D. Holmes, of The E. L. 

 Patch Company, were very kind to aid in supplying 

 the illustrations. The author also wishes to thank 

 Mr. Ernest F. Holt, of the Carnegie Museum, Mr. 

 Hugh A. Wing, of the University of Pittsburgh, and 

 Miss C. H. Watkins, of Ellicott City, Maryland, for 

 their invaluable aid in revising the manuscript. 



D.K.T. 



