6o Memoir Sears Foundation for Marine Research 



men; John Tee- Van, who furnished bibliographic citations; A. S. Romer, who assisted 

 us in determining classifications of major groups and who contributed summaries of the 

 various genera which occurred in earlier geologic periods; Ludlow Griscom and J. A. 

 Peters, who assisted us in the solution of puzzling questions regarding scientific nomen- 

 clature; H. W. Fowler, J. T. Nichols and L. P. Schultz, for their assistaiice; and 

 to the late Thomas Barbour, not only for putting the collections of the Museum of 

 Comparative Zoology so freely at our disposal, but for constant encouragement and 

 personal help in many ways. 



GENERAL DISCUSSION 



Scope of Study. The following pages give descriptions, illustrations, life histories and geo- 

 graphic distribution, as well as lists of published citations, for all species of sharks so far 

 known on the western side of the North Atlantic. In some genera represented within these 

 geographic limits, a few additional species occurring in the western South Atlantic but not 

 reported as yet north of the equator are included as addenda. The pertinent characteriza- 

 tions of the suborders and families, as well as the keys to major groups and genera, cover 

 the sharks as a whole and in some cases this applies to the species keys within genera. How- 

 ever, it seems wiser in other cases to limit them geographically until the relationships of 

 species from the western North Atlantic to those of adjacent parts of the ocean are clarified. 



Descriptions. The descriptions are based on the Study Material listed under each 

 species, except for Pseudotriakis microdon and Echinorhinus brucus, no specimens of which 

 were available. The discussions of habits and geographic distribution are based on data of 

 our Study Material, on information submitted to us through the co-operation of numerous 

 correspondents, checked in many cases by our own observations, and on previously pub- 

 lished accounts. 



Keys. The keys, whether to higher groups or to genera and species, have been ar- 

 ranged solely for the purpose of facilitating the identification of any shark. Therefore, 

 we have selected as alternative characters those that are most easily visible and measurable. 

 Our personal views on phylogeny are not discussed. Species within a genus are presented 

 in alphabetical sequence. 



References. All citations listed in the references, with the few exceptions noted, were 

 consulted in the original through the kind co-operation of the following libraries and insti- 

 tutions: Museum of Comparative Zoology and other departments of Harvard University; 

 American Academy of Arts and Sciences; Yale University; United States Fish and Wild- 

 life Service; Library of Congress; American Museum of Natural History; American 

 Philosophical Society; and Massachusetts Institute of Technology.^ 



Sources of Material. The well-rounded collection of sharks from many parts of the 

 world, preserved in the Museum of Comparative Zoology, has been our chief source of 



I. For pre-Linnaean names and references, see Garman (Mem. Harv. Mus. comp. Zool., 36, 1913). 



