562 PROCEEDINGS OF THE NATIONAL MUSEUM vol. us 



J. L. B. Smith (DIRU) ; R. R. Rofen, A. Fehlman, and W. L. Chan 

 (GVF); A. Ben-Tuvia (HUI); T. Monod and F. Paraiso (IFAN); 

 J. P. Gosse (IRSN); G. Krefft (ISH); G. Deckert (ISZZ); G. W. 

 Mead and M. Dick (MCZ); M. L. Bauchot (MNHN); M. Poll 

 (MRAC); W. Klausewitz and F. Rossel (NFIS); P. Kahsbauer 

 (NMV) ; G. Mack and A. Bartholomai (QMB) ; M. Boeseman (RNH) ; 

 R. Rosenblatt (SIO); H. Janus (SMNS) ; C. FHl (SMW); G. S. 

 Myers (SU) ; B. W. Walker (UCLA) ; C. R. Robins and W. R. Court- 

 enay, Jr. (UMML) ; R. M. Bailey (UMMZ) ; J. D'Aubrey (UND); 

 J. E. Randall (University of Puerto Rico); J. Nielsen (UZMK); 

 W. Ladiges (ZSZM). 



Radiographs were made in Europe and Australia with the help of 

 the following, to whom I express my sincere appreciation: F. Meier, 

 Roentgen Institut, Stuttgart; R. Pobisch, Tierarzliche Hochschule, 

 Vienna; J. P. Gasc, Laboratoire d'Anatomie Compare, Paris; Drs. 

 Leloup and Vastesaeger, Hopital d'lxelles, Belgium; P. DuUemeijer 

 and Mr. Simons, Zoologisch Laboratorium, Leiden, Holland; P. 

 R0nne, Biofysisk Lab, Copenhagen; R. Prevot and K. J. Thiemann, 

 Eppendorf, Hamburg; K. L. Schmidt and R. Lingemann, St. Mallins 

 Krankenhaus, Frankfurt; N. Mackintosh and assistants. University 

 of Sydney; Dr. Tod and assistants, Brisbane General Hospital, 

 Australia. 



The drawings of the sharks were done by my generous colleague 

 J. A. F. Garrick, and the shark teeth, by Dorothea B. Schultz. 



Stewart Springer (no relation) read the manuscript and offered 

 valuable criticisms. 



During the course of the study I had the good fortune of having 

 numerous discussions with, and suggestions from, J. A. F. Garrick. 

 His perceptive comments and criticisms were of great value in im- 

 proving the work and the manuscript. 



This investigation was made possible by funds supplied on a con- 

 tract, ONR 1354(09), between the Biology Branch of the Office of 

 Naval Research and the Smithsonian Institution, and administered by 

 Leonard P. Schultz. Dr. Schultz suggested the problem and greatly 

 facilitated my work by his encouragement and his expeditious han- 

 dhng of the many administrative matters that arose. 



Methods and Definitions 



Measurements. — Measurements on sharks are notoriously difficult 

 to obtain with accuracy, and it is rare that one investigator can 

 reproduce exactly another's measurements or even his own; never- 

 theless, proportions based on measurements are one of the few types 

 of characters available for the description of sharks. But many 

 errors originate in the twisted and distorted shapes that result from 



